feat(calendar): add birthday integration from contacts service

- Add birthdaysStore to fetch and manage birthdays from contacts API
- Add BirthdayPopover component with contact details and link to contacts app
- Integrate birthdays into WeekView, MonthView, and DayView as all-day events
- Add settings for showBirthdays and showBirthdayAge toggles
- Add reactive $effect in layout to load birthdays when setting is enabled
- Add /contacts/birthdays endpoint to contacts backend
- Configure PUBLIC_CONTACTS_API_URL env variable for calendar app

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/calendar/apps/web/src/lib/api/birthdays.ts

@@ -0,0 +1,100 @@
+/**
+ * Cross-App API Client for Contacts Backend - Birthday Data
+ * Allows Calendar app to fetch contact birthdays for display
+ */
+
+import { env } from '$env/dynamic/public';
+import { createApiClient } from './base-client';
+
+const CONTACTS_API_BASE = env.PUBLIC_CONTACTS_API_URL || 'http://localhost:3015';
+
+const contactsClient = createApiClient({
+	baseUrl: CONTACTS_API_BASE,
+	apiPrefix: '/api/v1',
+});
+
+// ============================================
+// Types for Birthday Integration
+// ============================================
+
+/**
+ * Lightweight contact data for birthday display
+ * Only essential fields from Contacts API
+ */
+export interface ContactBirthdaySummary {
+	id: string;
+	displayName: string | null;
+	firstName: string | null;
+	lastName: string | null;
+	birthday: string; // YYYY-MM-DD format
+	photoUrl: string | null;
+}
+
+/**
+ * Birthday event for calendar display
+ * Generated from ContactBirthdaySummary with display date
+ */
+export interface BirthdayEvent {
+	id: string; // Format: birthday-{contactId}-{date}
+	contactId: string;
+	title: string; // "{Name}'s Geburtstag"
+	displayName: string;
+	photoUrl: string | null;
+	birthday: string; // Original birthday date
+	age: number; // Age on this birthday (0 if birth year unknown)
+	startTime: string; // ISO date of the birthday occurrence
+	endTime: string; // Same as startTime (all-day event)
+	isAllDay: true;
+	isBirthday: true; // Type discriminator
+	calendarId: string; // Virtual calendar ID
+}
+
+// ============================================
+// API Response Types
+// ============================================
+
+interface BirthdaysResponse {
+	contacts: ContactBirthdaySummary[];
+}
+
+// ============================================
+// API Functions
+// ============================================
+
+const fetchContactsApi = contactsClient.fetchApi;
+
+/**
+ * Fetch all contacts with birthdays from Contacts service
+ */
+export async function getBirthdays(): Promise<{
+	data: ContactBirthdaySummary[] | null;
+	error: Error | null;
+}> {
+	const result = await fetchContactsApi<BirthdaysResponse>('/contacts/birthdays');
+	return {
+		data: result.data?.contacts || null,
+		error: result.error,
+	};
+}
+
+// ============================================
+// Helper Functions
+// ============================================
+
+/**
+ * Get display name from contact, with fallback
+ */
+export function getContactDisplayName(contact: ContactBirthdaySummary): string {
+	if (contact.displayName) return contact.displayName;
+	const fullName = [contact.firstName, contact.lastName].filter(Boolean).join(' ');
+	return fullName || 'Unbekannt';
+}
+
+/**
+ * Birthday calendar constants
+ */
+export const BIRTHDAY_CALENDAR = {
+	id: '__birthdays__',
+	name: 'Geburtstage',
+	color: '#EC4899', // Pink
+} as const;

apps/calendar/apps/web/src/lib/components/birthday/BirthdayPopover.svelte

@@ -0,0 +1,269 @@
+<script lang="ts">
+	import { env } from '$env/dynamic/public';
+	import type { BirthdayEvent } from '$lib/api/birthdays';
+	import { settingsStore } from '$lib/stores/settings.svelte';
+	import { X, User, ExternalLink, Cake } from 'lucide-svelte';
+	import { format, parseISO } from 'date-fns';
+	import { de } from 'date-fns/locale';
+
+	interface Props {
+		birthday: BirthdayEvent;
+		position: { x: number; y: number };
+		onClose: () => void;
+	}
+
+	let { birthday, position, onClose }: Props = $props();
+
+	const CONTACTS_WEB_URL = env.PUBLIC_CONTACTS_WEB_URL || 'http://localhost:5184';
+	const contactUrl = `${CONTACTS_WEB_URL}/contacts/${birthday.contactId}`;
+
+	// Format the original birthday date
+	let birthdayDateFormatted = $derived(() => {
+		try {
+			const date = parseISO(birthday.birthday);
+			return format(date, 'd. MMMM', { locale: de });
+		} catch {
+			return birthday.birthday;
+		}
+	});
+
+	// Calculate popover position to stay within viewport
+	let adjustedPosition = $derived(() => {
+		const popoverWidth = 280;
+		const popoverHeight = 200;
+		const padding = 16;
+
+		let x = position.x;
+		let y = position.y;
+
+		// Check right boundary
+		if (x + popoverWidth + padding > window.innerWidth) {
+			x = window.innerWidth - popoverWidth - padding;
+		}
+
+		// Check bottom boundary
+		if (y + popoverHeight + padding > window.innerHeight) {
+			y = position.y - popoverHeight - 8; // Show above
+		}
+
+		// Check left boundary
+		if (x < padding) {
+			x = padding;
+		}
+
+		// Check top boundary
+		if (y < padding) {
+			y = padding;
+		}
+
+		return { x, y };
+	});
+
+	function handleBackdropClick(e: MouseEvent) {
+		if (e.target === e.currentTarget) {
+			onClose();
+		}
+	}
+
+	function handleKeydown(e: KeyboardEvent) {
+		if (e.key === 'Escape') {
+			onClose();
+		}
+	}
+</script>
+
+<svelte:window onkeydown={handleKeydown} />
+
+<!-- Backdrop -->
+<div
+	class="fixed inset-0 z-50"
+	onclick={handleBackdropClick}
+	onkeydown={(e) => e.key === 'Escape' && onClose()}
+	role="button"
+	tabindex="-1"
+>
+	<!-- Popover -->
+	<div
+		class="birthday-popover"
+		style="left: {adjustedPosition().x}px; top: {adjustedPosition().y}px;"
+		role="dialog"
+		aria-label="Geburtstag Details"
+	>
+		<!-- Header -->
+		<div class="popover-header">
+			<div class="header-content">
+				{#if birthday.photoUrl}
+					<img src={birthday.photoUrl} alt={birthday.displayName} class="contact-avatar" />
+				{:else}
+					<div class="contact-avatar-placeholder">
+						<Cake size={24} />
+					</div>
+				{/if}
+				<div class="header-info">
+					<h3 class="contact-name">{birthday.displayName}</h3>
+					{#if settingsStore.showBirthdayAge && birthday.age > 0}
+						<p class="contact-age">wird {birthday.age} Jahre alt</p>
+					{/if}
+				</div>
+			</div>
+			<button type="button" class="close-btn" onclick={onClose} aria-label="Schließen">
+				<X size={18} />
+			</button>
+		</div>
+
+		<!-- Content -->
+		<div class="popover-content">
+			<div class="info-row">
+				<Cake size={16} class="info-icon" />
+				<span>Geburtstag: {birthdayDateFormatted()}</span>
+			</div>
+		</div>
+
+		<!-- Actions -->
+		<div class="popover-actions">
+			<a href={contactUrl} target="_blank" rel="noopener noreferrer" class="action-btn primary">
+				<User size={16} />
+				<span>Kontakt öffnen</span>
+				<ExternalLink size={14} class="external-icon" />
+			</a>
+		</div>
+	</div>
+</div>
+
+<style>
+	.birthday-popover {
+		position: fixed;
+		width: 280px;
+		background: hsl(var(--color-surface));
+		border: 1px solid hsl(var(--color-border));
+		border-radius: 12px;
+		box-shadow: 0 8px 24px hsl(var(--color-foreground) / 0.15);
+		overflow: hidden;
+		z-index: 51;
+	}
+
+	.popover-header {
+		display: flex;
+		align-items: flex-start;
+		justify-content: space-between;
+		padding: 1rem;
+		background: linear-gradient(135deg, #ec4899 0%, #f472b6 100%);
+		color: white;
+	}
+
+	.header-content {
+		display: flex;
+		align-items: center;
+		gap: 0.75rem;
+	}
+
+	.contact-avatar {
+		width: 48px;
+		height: 48px;
+		border-radius: 50%;
+		object-fit: cover;
+		border: 2px solid white;
+	}
+
+	.contact-avatar-placeholder {
+		width: 48px;
+		height: 48px;
+		border-radius: 50%;
+		background: hsl(var(--color-surface) / 0.2);
+		display: flex;
+		align-items: center;
+		justify-content: center;
+		border: 2px solid white;
+		color: white;
+	}
+
+	.header-info {
+		flex: 1;
+		min-width: 0;
+	}
+
+	.contact-name {
+		font-size: 1rem;
+		font-weight: 600;
+		margin: 0;
+		white-space: nowrap;
+		overflow: hidden;
+		text-overflow: ellipsis;
+	}
+
+	.contact-age {
+		font-size: 0.875rem;
+		margin: 0.125rem 0 0;
+		opacity: 0.9;
+	}
+
+	.close-btn {
+		background: hsl(var(--color-surface) / 0.2);
+		border: none;
+		border-radius: 50%;
+		width: 28px;
+		height: 28px;
+		display: flex;
+		align-items: center;
+		justify-content: center;
+		cursor: pointer;
+		color: white;
+		transition: background 0.2s ease;
+	}
+
+	.close-btn:hover {
+		background: hsl(var(--color-surface) / 0.3);
+	}
+
+	.popover-content {
+		padding: 1rem;
+	}
+
+	.info-row {
+		display: flex;
+		align-items: center;
+		gap: 0.5rem;
+		font-size: 0.875rem;
+		color: hsl(var(--color-muted-foreground));
+	}
+
+	.info-row :global(.info-icon) {
+		color: #ec4899;
+		flex-shrink: 0;
+	}
+
+	.popover-actions {
+		padding: 0.75rem 1rem 1rem;
+		border-top: 1px solid hsl(var(--color-border));
+	}
+
+	.action-btn {
+		display: flex;
+		align-items: center;
+		justify-content: center;
+		gap: 0.5rem;
+		width: 100%;
+		padding: 0.625rem 1rem;
+		border: none;
+		border-radius: 8px;
+		font-size: 0.875rem;
+		font-weight: 500;
+		cursor: pointer;
+		text-decoration: none;
+		transition: all 0.2s ease;
+	}
+
+	.action-btn.primary {
+		background: #ec4899;
+		color: white;
+	}
+
+	.action-btn.primary:hover {
+		background: #db2777;
+	}
+
+	.action-btn :global(.external-icon) {
+		opacity: 0.7;
+		margin-left: auto;
+	}
+</style>

apps/calendar/apps/web/src/lib/components/calendar/DayView.svelte

@@ -6,6 +6,8 @@
 	import { searchStore } from '$lib/stores/search.svelte';
 	import { todosStore, type Task } from '$lib/stores/todos.svelte';
 	import { eventContextMenuStore } from '$lib/stores/eventContextMenu.svelte';
+	import { birthdaysStore, type BirthdayEvent } from '$lib/stores/birthdays.svelte';
+	import BirthdayPopover from '$lib/components/birthday/BirthdayPopover.svelte';
 	import {
 		useVisibleHours,
 		useCurrentTimeIndicator,
@@ -131,6 +133,28 @@
 
 	let blockAllDayEvents = $derived(allDayEvents.filter((e) => getEventDisplayMode(e) === 'block'));
 
+	// Birthday Popover State
+	let selectedBirthday = $state<BirthdayEvent | null>(null);
+	let birthdayPopoverPosition = $state<{ x: number; y: number }>({ x: 0, y: 0 });
+
+	// Get birthdays for current day (if enabled in settings)
+	let birthdays = $derived.by(() => {
+		if (!settingsStore.showBirthdays) return [];
+		return birthdaysStore.getBirthdaysForDay(viewStore.currentDate);
+	});
+
+	// Handle birthday click - show popover
+	function handleBirthdayClick(birthday: BirthdayEvent, e: MouseEvent) {
+		e.stopPropagation();
+		selectedBirthday = birthday;
+		birthdayPopoverPosition = { x: e.clientX, y: e.clientY };
+	}
+
+	// Close birthday popover
+	function closeBirthdayPopover() {
+		selectedBirthday = null;
+	}
+
 	// ============================================================================
 	// Drag & Drop State
 	// ============================================================================
@@ -729,8 +753,8 @@
 </script>
 
 <div class="day-view">
-	<!-- Header-style all-day events -->
+	<!-- Header-style all-day events and birthdays -->
-	{#if headerAllDayEvents.length > 0}
+	{#if headerAllDayEvents.length > 0 || birthdays.length > 0}
 		<div class="all-day-section">
 			<div class="time-gutter">
 				<span class="all-day-label">Ganztägig</span>
@@ -747,6 +771,18 @@
 						{event.title}
 					</button>
 				{/each}
+				<!-- Birthdays -->
+				{#each birthdays as birthday}
+					<button
+						class="all-day-event birthday-event"
+						onclick={(e) => handleBirthdayClick(birthday, e)}
+					>
+						🎂 {birthday.displayName}
+						{#if settingsStore.showBirthdayAge && birthday.age > 0}
+							<span class="birthday-age">({birthday.age})</span>
+						{/if}
+					</button>
+				{/each}
 			</div>
 		</div>
 	{/if}
@@ -909,6 +945,15 @@
 <!-- Event Context Menu -->
 <EventContextMenu onEdit={handleContextMenuEdit} />
 
+<!-- Birthday Popover -->
+{#if selectedBirthday}
+	<BirthdayPopover
+		birthday={selectedBirthday}
+		position={birthdayPopoverPosition}
+		onClose={closeBirthdayPopover}
+	/>
+{/if}
+
 <style>
 	.day-view {
 		display: flex;
@@ -1238,4 +1283,18 @@
 		opacity: 1;
 		height: 5px;
 	}
+
+	/* Birthday events in all-day row */
+	.all-day-event.birthday-event {
+		background: linear-gradient(135deg, #ec4899 0%, #f472b6 100%);
+	}
+
+	.all-day-event.birthday-event:hover {
+		opacity: 0.9;
+	}
+
+	.birthday-age {
+		opacity: 0.85;
+		font-size: 0.7rem;
+	}
 </style>

apps/calendar/apps/web/src/lib/components/calendar/MonthView.svelte

@@ -5,8 +5,10 @@
 	import { settingsStore } from '$lib/stores/settings.svelte';
 	import { searchStore } from '$lib/stores/search.svelte';
 	import { todosStore } from '$lib/stores/todos.svelte';
+	import { birthdaysStore, type BirthdayEvent } from '$lib/stores/birthdays.svelte';
 	import { eventContextMenuStore } from '$lib/stores/eventContextMenu.svelte';
 	import TodoDayCell from './TodoDayCell.svelte';
+	import BirthdayPopover from '$lib/components/birthday/BirthdayPopover.svelte';
 	import { goto } from '$app/navigation';
 	import {
 		format,
@@ -259,6 +261,27 @@
 		if (eventsStore.isDraftEvent(event.id)) return;
 		eventContextMenuStore.show(event, e.clientX, e.clientY);
 	}
+
+	// ============================================================================
+	// Birthday Functions
+	// ============================================================================
+	let selectedBirthday = $state<BirthdayEvent | null>(null);
+	let birthdayPopoverPosition = $state<{ x: number; y: number }>({ x: 0, y: 0 });
+
+	function getBirthdaysForDay(day: Date): BirthdayEvent[] {
+		if (!settingsStore.showBirthdays) return [];
+		return birthdaysStore.getBirthdaysForDay(day);
+	}
+
+	function handleBirthdayClick(birthday: BirthdayEvent, e: MouseEvent) {
+		e.stopPropagation();
+		selectedBirthday = birthday;
+		birthdayPopoverPosition = { x: e.clientX, y: e.clientY };
+	}
+
+	function closeBirthdayPopover() {
+		selectedBirthday = null;
+	}
 </script>
 
 <div class="month-view" style="--column-count: {columnCount}" bind:this={monthViewRef}>
@@ -338,6 +361,23 @@
 								</div>
 							{/each}
 
+							<!-- Birthdays -->
+							{#each getBirthdaysForDay(day) as birthday}
+								<!-- svelte-ignore a11y_click_events_have_key_events -->
+								<div
+									class="event-pill birthday-pill"
+									onclick={(e) => handleBirthdayClick(birthday, e)}
+									role="button"
+									tabindex="0"
+								>
+									🎂
+									<span class="event-title">{birthday.displayName}</span>
+									{#if settingsStore.showBirthdayAge && birthday.age > 0}
+										<span class="birthday-age">({birthday.age})</span>
+									{/if}
+								</div>
+							{/each}
+
 							{#if getAllEventsForDay(day).length > 3}
 								<button class="more-events" onclick={(e) => handleMoreClick(day, e)}>
 									{$_('views.moreEvents', {
@@ -353,6 +393,15 @@
 	</div>
 </div>
 
+<!-- Birthday Popover -->
+{#if selectedBirthday}
+	<BirthdayPopover
+		birthday={selectedBirthday}
+		position={birthdayPopoverPosition}
+		onClose={closeBirthdayPopover}
+	/>
+{/if}
+
 <style>
 	.month-view {
 		display: flex;
@@ -537,4 +586,19 @@
 		outline: 2px dashed hsl(var(--color-primary));
 		outline-offset: -2px;
 	}
+
+	/* Birthday pills */
+	.event-pill.birthday-pill {
+		background: linear-gradient(135deg, #ec4899 0%, #f472b6 100%);
+		cursor: pointer;
+	}
+
+	.event-pill.birthday-pill:hover {
+		opacity: 0.9;
+	}
+
+	.birthday-age {
+		opacity: 0.85;
+		font-size: 0.65rem;
+	}
 </style>

apps/calendar/apps/web/src/lib/components/calendar/WeekView.svelte

@@ -5,7 +5,9 @@
 	import { settingsStore } from '$lib/stores/settings.svelte';
 	import { searchStore } from '$lib/stores/search.svelte';
 	import { todosStore, type Task } from '$lib/stores/todos.svelte';
+	import { birthdaysStore, type BirthdayEvent } from '$lib/stores/birthdays.svelte';
 	import { eventContextMenuStore } from '$lib/stores/eventContextMenu.svelte';
+	import BirthdayPopover from '$lib/components/birthday/BirthdayPopover.svelte';
 	import {
 		useVisibleHours,
 		useCurrentTimeIndicator,
@@ -118,6 +120,33 @@
 	// Reference to the days container for position calculations
 	let daysContainerEl: HTMLDivElement;
 
+	// Birthday Popover State
+	let selectedBirthday = $state<BirthdayEvent | null>(null);
+	let birthdayPopoverPosition = $state<{ x: number; y: number }>({ x: 0, y: 0 });
+
+	// Get birthdays for a day (if enabled in settings)
+	function getBirthdaysForDay(day: Date): BirthdayEvent[] {
+		if (!settingsStore.showBirthdays) return [];
+		return birthdaysStore.getBirthdaysForDay(day);
+	}
+
+	// Check if there are any birthdays to show in the all-day row
+	let hasAnyBirthdays = $derived(
+		settingsStore.showBirthdays && days.some((day) => getBirthdaysForDay(day).length > 0)
+	);
+
+	// Handle birthday click - show popover
+	function handleBirthdayClick(birthday: BirthdayEvent, e: MouseEvent) {
+		e.stopPropagation();
+		selectedBirthday = birthday;
+		birthdayPopoverPosition = { x: e.clientX, y: e.clientY };
+	}
+
+	// Close birthday popover
+	function closeBirthdayPopover() {
+		selectedBirthday = null;
+	}
+
 	function getEventsForDay(day: Date) {
 		// Filter by visible calendars first
 		const visibleCalendarIds = new Set(calendarsStore.visibleCalendars.map((c) => c.id));
@@ -888,8 +917,8 @@
 			{/each}
 		</div>
 
-		<!-- All-day events row (only shown when there are header-mode all-day events) -->
+		<!-- All-day events row (shown when there are header-mode all-day events or birthdays) -->
-		{#if hasAnyHeaderAllDayEvents}
+		{#if hasAnyHeaderAllDayEvents || hasAnyBirthdays}
 			<div class="all-day-row">
 				<div class="time-gutter">
 					{#if settingsStore.showWeekNumbers}
@@ -909,6 +938,18 @@
 								{event.title}
 							</button>
 						{/each}
+						<!-- Birthdays -->
+						{#each getBirthdaysForDay(day) as birthday}
+							<button
+								class="all-day-event birthday-event"
+								onclick={(e) => handleBirthdayClick(birthday, e)}
+							>
+								🎂 {birthday.displayName}
+								{#if settingsStore.showBirthdayAge && birthday.age > 0}
+									<span class="birthday-age">({birthday.age})</span>
+								{/if}
+							</button>
+						{/each}
 					</div>
 				{/each}
 			</div>
@@ -1107,6 +1148,15 @@
 
 <EventContextMenu onEdit={handleContextMenuEdit} />
 
+<!-- Birthday Popover -->
+{#if selectedBirthday}
+	<BirthdayPopover
+		birthday={selectedBirthday}
+		position={birthdayPopoverPosition}
+		onClose={closeBirthdayPopover}
+	/>
+{/if}
+
 <style>
 	.week-view {
 		display: flex;
@@ -1165,6 +1215,20 @@
 		filter: grayscale(0.3);
 	}
 
+	/* Birthday events in all-day row */
+	.all-day-event.birthday-event {
+		background: linear-gradient(135deg, #ec4899 0%, #f472b6 100%);
+	}
+
+	.all-day-event.birthday-event:hover {
+		opacity: 0.9;
+	}
+
+	.birthday-age {
+		opacity: 0.85;
+		font-size: 0.7rem;
+	}
+
 	/* Block-style all-day events (displayed as full-day blocks in the grid) */
 	.all-day-block-event {
 		position: absolute;

apps/calendar/apps/web/src/lib/stores/birthdays.svelte.ts

@@ -0,0 +1,219 @@
+/**
+ * Birthdays Store - Manages contact birthdays for calendar display
+ * Cross-app integration with Contacts Backend (similar to todosStore)
+ */
+
+import { browser } from '$app/environment';
+import * as api from '$lib/api/birthdays';
+import type { ContactBirthdaySummary, BirthdayEvent } from '$lib/api/birthdays';
+import { getContactDisplayName, BIRTHDAY_CALENDAR } from '$lib/api/birthdays';
+import { differenceInYears, isSameDay, isWithinInterval, parseISO, format } from 'date-fns';
+
+// Re-export types for convenience
+export type { ContactBirthdaySummary, BirthdayEvent };
+
+// ============================================
+// State
+// ============================================
+
+let birthdays = $state<ContactBirthdaySummary[]>([]);
+let loading = $state(false);
+let error = $state<string | null>(null);
+let serviceAvailable = $state(true);
+let lastFetchTime = $state<number>(0);
+
+// Cache settings
+const CACHE_TTL = 5 * 60 * 1000; // 5 minutes
+
+// ============================================
+// Store Export
+// ============================================
+
+export const birthdaysStore = {
+	// ========== Getters ==========
+	get birthdays() {
+		return birthdays ?? [];
+	},
+	get loading() {
+		return loading;
+	},
+	get error() {
+		return error;
+	},
+	get serviceAvailable() {
+		return serviceAvailable;
+	},
+	get calendarId() {
+		return BIRTHDAY_CALENDAR.id;
+	},
+	get calendarColor() {
+		return BIRTHDAY_CALENDAR.color;
+	},
+	get calendarName() {
+		return BIRTHDAY_CALENDAR.name;
+	},
+
+	// ========== Birthday Getters ==========
+
+	/**
+	 * Get birthday events for a specific day
+	 * Matches by month and day (ignores year)
+	 */
+	getBirthdaysForDay(date: Date): BirthdayEvent[] {
+		const currentBirthdays = birthdays ?? [];
+		if (!Array.isArray(currentBirthdays) || currentBirthdays.length === 0) return [];
+
+		return currentBirthdays
+			.filter((contact) => {
+				if (!contact.birthday) return false;
+				const birthdayDate = parseISO(contact.birthday);
+				// Compare month and day only
+				return (
+					birthdayDate.getMonth() === date.getMonth() && birthdayDate.getDate() === date.getDate()
+				);
+			})
+			.map((contact) => this.toBirthdayEvent(contact, date));
+	},
+
+	/**
+	 * Get birthday events within a date range
+	 */
+	getBirthdaysInRange(start: Date, end: Date): BirthdayEvent[] {
+		const currentBirthdays = birthdays ?? [];
+		if (!Array.isArray(currentBirthdays) || currentBirthdays.length === 0) return [];
+
+		const events: BirthdayEvent[] = [];
+		const current = new Date(start);
+
+		// Iterate through each day in range
+		while (current <= end) {
+			const dayBirthdays = this.getBirthdaysForDay(current);
+			events.push(...dayBirthdays);
+			current.setDate(current.getDate() + 1);
+		}
+
+		return events;
+	},
+
+	/**
+	 * Check if a specific day has any birthdays
+	 */
+	hasBirthdaysOnDay(date: Date): boolean {
+		const currentBirthdays = birthdays ?? [];
+		if (!Array.isArray(currentBirthdays)) return false;
+
+		return currentBirthdays.some((contact) => {
+			if (!contact.birthday) return false;
+			const birthdayDate = parseISO(contact.birthday);
+			return (
+				birthdayDate.getMonth() === date.getMonth() && birthdayDate.getDate() === date.getDate()
+			);
+		});
+	},
+
+	/**
+	 * Get upcoming birthdays (next N days)
+	 */
+	getUpcomingBirthdays(days: number = 30): BirthdayEvent[] {
+		const start = new Date();
+		const end = new Date();
+		end.setDate(end.getDate() + days);
+		return this.getBirthdaysInRange(start, end);
+	},
+
+	/**
+	 * Convert contact to birthday event
+	 */
+	toBirthdayEvent(contact: ContactBirthdaySummary, displayDate: Date): BirthdayEvent {
+		const displayName = getContactDisplayName(contact);
+		const birthdayDate = parseISO(contact.birthday);
+		const birthYear = birthdayDate.getFullYear();
+
+		// Calculate age (0 if year seems invalid, e.g., 1900 default)
+		let age = differenceInYears(displayDate, birthdayDate);
+		if (birthYear < 1900 || birthYear > new Date().getFullYear()) {
+			age = 0; // Unknown birth year
+		}
+
+		const dateStr = format(displayDate, 'yyyy-MM-dd');
+
+		return {
+			id: `birthday-${contact.id}-${dateStr}`,
+			contactId: contact.id,
+			title: `${displayName}`,
+			displayName,
+			photoUrl: contact.photoUrl,
+			birthday: contact.birthday,
+			age,
+			startTime: displayDate.toISOString(),
+			endTime: displayDate.toISOString(),
+			isAllDay: true,
+			isBirthday: true,
+			calendarId: BIRTHDAY_CALENDAR.id,
+		};
+	},
+
+	// ========== API Methods ==========
+
+	/**
+	 * Fetch birthdays from Contacts service
+	 * Uses cache to avoid frequent refetches
+	 */
+	async fetchBirthdays(force = false) {
+		if (!browser) return;
+
+		// Use cache if still valid
+		if (!force && Date.now() - lastFetchTime < CACHE_TTL && birthdays.length > 0) {
+			return;
+		}
+
+		loading = true;
+		error = null;
+
+		const result = await api.getBirthdays();
+
+		if (result.error) {
+			error = result.error.message;
+			serviceAvailable = false;
+		} else {
+			birthdays = result.data || [];
+			serviceAvailable = true;
+			lastFetchTime = Date.now();
+		}
+
+		loading = false;
+	},
+
+	/**
+	 * Check if Contacts service is available
+	 */
+	async checkServiceHealth(): Promise<boolean> {
+		const result = await api.getBirthdays();
+		serviceAvailable = !result.error;
+		return serviceAvailable;
+	},
+
+	/**
+	 * Clear birthdays cache
+	 */
+	clear() {
+		birthdays = [];
+		lastFetchTime = 0;
+	},
+
+	/**
+	 * Get contact by ID from cached birthdays
+	 */
+	getContactById(id: string): ContactBirthdaySummary | undefined {
+		const currentBirthdays = birthdays ?? [];
+		if (!Array.isArray(currentBirthdays)) return undefined;
+		return currentBirthdays.find((c) => c.id === id);
+	},
+
+	/**
+	 * Count of contacts with birthdays
+	 */
+	get count(): number {
+		return birthdays?.length ?? 0;
+	},
+};

apps/calendar/apps/web/src/lib/stores/settings.svelte.ts

@@ -35,6 +35,10 @@ export interface CalendarAppSettings {
 	dateStripCompact: boolean; // Use compact/smaller DateStrip
 	dateStripShowWeekNumbers: boolean; // Show week numbers at start of week
 
+	// Birthday settings (cross-app integration with Contacts)
+	showBirthdays: boolean; // Show contact birthdays in calendar
+	showBirthdayAge: boolean; // Show age in birthday events
+
 	// UI settings
 	sidebarCollapsed: boolean;
 
@@ -61,6 +65,9 @@ const DEFAULT_SETTINGS: CalendarAppSettings = {
 	dateStripShowMonthDividers: true,
 	dateStripCompact: false,
 	dateStripShowWeekNumbers: false,
+	// Birthday defaults
+	showBirthdays: true,
+	showBirthdayAge: true,
 	// UI defaults
 	sidebarCollapsed: false,
 	defaultEventDuration: 60,
@@ -182,6 +189,13 @@ export const settingsStore = {
 	get dateStripShowWeekNumbers() {
 		return settings.dateStripShowWeekNumbers;
 	},
+	// Birthday settings
+	get showBirthdays() {
+		return settings.showBirthdays;
+	},
+	get showBirthdayAge() {
+		return settings.showBirthdayAge;
+	},
 	get defaultEventDuration() {
 		return settings.defaultEventDuration;
 	},

apps/calendar/apps/web/src/routes/(app)/+layout.svelte

@@ -23,6 +23,8 @@
 	import { eventsStore } from '$lib/stores/events.svelte';
 	import { eventTagsStore } from '$lib/stores/event-tags.svelte';
 	import { settingsStore } from '$lib/stores/settings.svelte';
+	import { birthdaysStore } from '$lib/stores/birthdays.svelte';
+	import { browser } from '$app/environment';
 	import {
 		THEME_DEFINITIONS,
 		DEFAULT_THEME_VARIANTS,
@@ -282,6 +284,13 @@
 		goto(`/?event=${event.id}`);
 	}
 
+	// Reactive effect: load birthdays when setting is enabled
+	$effect(() => {
+		if (browser && settingsStore.showBirthdays && authStore.isAuthenticated) {
+			birthdaysStore.fetchBirthdays();
+		}
+	});
+
 	onMount(async () => {
 		// Redirect to login if not authenticated
 		if (!authStore.isAuthenticated) {
@@ -300,6 +309,8 @@
 		await eventTagsStore.fetchTags();
 		await userSettings.load();
 
+		// Note: Birthdays are loaded via reactive $effect when showBirthdays is enabled
+
 		// Redirect to start page if on root and a custom start page is set
 		const currentPath = window.location.pathname;
 		if (currentPath === '/' && userSettings.startPage && userSettings.startPage !== '/') {

apps/calendar/apps/web/src/routes/(app)/settings/+page.svelte

@@ -7,7 +7,13 @@
 	import type { TimeFormat, AllDayDisplayMode } from '$lib/stores/settings.svelte';
 	import { calendarsStore } from '$lib/stores/calendars.svelte';
 	import { toast } from '$lib/stores/toast.svelte';
-	import { GlobalSettingsSection, SettingsSection, SettingsCard } from '@manacore/shared-ui';
+	import {
+		GlobalSettingsSection,
+		SettingsSection,
+		SettingsCard,
+		FilterDropdown,
+		type FilterDropdownOption,
+	} from '@manacore/shared-ui';
 	import type { CalendarViewType, Calendar } from '@calendar/shared';
 
 	// Calendar management state
@@ -144,6 +150,47 @@
 		{ value: 60, label: '1 Stunde' },
 		{ value: 1440, label: '1 Tag' },
 	];
+
+	// FilterDropdown options
+	let viewOptions = $derived<FilterDropdownOption[]>(
+		Object.entries(viewLabels).map(([value, label]) => ({ value, label }))
+	);
+
+	let durationDropdownOptions = $derived<FilterDropdownOption[]>(
+		durationOptions.map((duration) => ({
+			value: String(duration),
+			label:
+				duration >= 60
+					? `${duration / 60} Stunde${duration > 60 ? 'n' : ''}`
+					: `${duration} Minuten`,
+		}))
+	);
+
+	let reminderDropdownOptions = $derived<FilterDropdownOption[]>(
+		reminderOptions.map((opt) => ({
+			value: String(opt.value),
+			label: opt.label,
+		}))
+	);
+
+	// Dynamic hour options (filtered by the other value)
+	let hourStartOptions = $derived<FilterDropdownOption[]>(
+		Array.from({ length: 24 }, (_, i) => i)
+			.filter((hour) => hour < settingsStore.dayEndHour)
+			.map((hour) => ({
+				value: String(hour),
+				label: `${hour.toString().padStart(2, '0')}:00`,
+			}))
+	);
+
+	let hourEndOptions = $derived<FilterDropdownOption[]>(
+		Array.from({ length: 24 }, (_, i) => i + 1)
+			.filter((hour) => hour > settingsStore.dayStartHour)
+			.map((hour) => ({
+				value: String(hour),
+				label: `${hour.toString().padStart(2, '0')}:00`,
+			}))
+	);
 </script>
 
 <svelte:head>
@@ -348,15 +395,12 @@
 						<span class="setting-label">Standard-Ansicht</span>
 						<span class="setting-description">Ansicht beim Öffnen des Kalenders</span>
 					</div>
-					<select
+					<FilterDropdown
-						class="select-input"
+						options={viewOptions}
 						value={settingsStore.defaultView}
-						onchange={(e) => handleViewChange(e.currentTarget.value as CalendarViewType)}
+						onChange={(v) => handleViewChange(v as CalendarViewType)}
-					>
+						placeholder="Ansicht wählen"
-						{#each Object.entries(viewLabels) as [value, label]}
+					/>
-							<option {value}>{label}</option>
-						{/each}
-					</select>
 				</div>
 
 				<div class="setting-item">
@@ -438,35 +482,23 @@
 						</div>
 						<div class="hour-range-inputs">
 							<div class="hour-input-group">
-								<label for="start-hour">Von</label>
+								<span class="hour-label">Von</span>
-								<select
+								<FilterDropdown
-									id="start-hour"
+									options={hourStartOptions}
-									class="select-input hour-select"
+									value={String(settingsStore.dayStartHour)}
-									value={settingsStore.dayStartHour}
+									onChange={(v) => settingsStore.set('dayStartHour', Number(v))}
-									onchange={(e) => settingsStore.set('dayStartHour', Number(e.currentTarget.value))}
+									placeholder="Start"
-								>
+								/>
-									{#each Array.from({ length: 24 }, (_, i) => i) as hour}
-										{#if hour < settingsStore.dayEndHour}
-											<option value={hour}>{hour.toString().padStart(2, '0')}:00</option>
-										{/if}
-									{/each}
-								</select>
 							</div>
 							<span class="hour-separator">–</span>
 							<div class="hour-input-group">
-								<label for="end-hour">Bis</label>
+								<span class="hour-label">Bis</span>
-								<select
+								<FilterDropdown
-									id="end-hour"
+									options={hourEndOptions}
-									class="select-input hour-select"
+									value={String(settingsStore.dayEndHour)}
-									value={settingsStore.dayEndHour}
+									onChange={(v) => settingsStore.set('dayEndHour', Number(v))}
-									onchange={(e) => settingsStore.set('dayEndHour', Number(e.currentTarget.value))}
+									placeholder="Ende"
-								>
+								/>
-									{#each Array.from({ length: 24 }, (_, i) => i + 1) as hour}
-										{#if hour > settingsStore.dayStartHour}
-											<option value={hour}>{hour.toString().padStart(2, '0')}:00</option>
-										{/if}
-									{/each}
-								</select>
 							</div>
 						</div>
 					</div>
@@ -517,19 +549,12 @@
 						<span class="setting-label">Standard-Dauer</span>
 						<span class="setting-description">Voreingestellte Dauer für neue Termine</span>
 					</div>
-					<select
+					<FilterDropdown
-						class="select-input"
+						options={durationDropdownOptions}
-						value={settingsStore.defaultEventDuration}
+						value={String(settingsStore.defaultEventDuration)}
-						onchange={(e) => handleEventDurationChange(Number(e.currentTarget.value))}
+						onChange={(v) => handleEventDurationChange(Number(v))}
-					>
+						placeholder="Dauer wählen"
-						{#each durationOptions as duration}
+					/>
-							<option value={duration}>
-								{duration >= 60
-									? `${duration / 60} Stunde${duration > 60 ? 'n' : ''}`
-									: `${duration} Minuten`}
-							</option>
-						{/each}
-					</select>
 				</div>
 
 				<div class="setting-item">
@@ -537,20 +562,68 @@
 						<span class="setting-label">Standard-Erinnerung</span>
 						<span class="setting-description">Voreingestellte Erinnerung für neue Termine</span>
 					</div>
-					<select
+					<FilterDropdown
-						class="select-input"
+						options={reminderDropdownOptions}
-						value={settingsStore.defaultReminder}
+						value={String(settingsStore.defaultReminder)}
-						onchange={(e) => handleReminderChange(Number(e.currentTarget.value))}
+						onChange={(v) => handleReminderChange(Number(v))}
-					>
+						placeholder="Erinnerung wählen"
-						{#each reminderOptions as option}
+					/>
-							<option value={option.value}>{option.label}</option>
-						{/each}
-					</select>
 				</div>
 			</div>
 		</SettingsCard>
 	</SettingsSection>
 
+	<!-- Geburtstage -->
+	<SettingsSection title="Geburtstage">
+		{#snippet icon()}
+			<svg fill="none" stroke="currentColor" viewBox="0 0 24 24">
+				<path
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					stroke-width="2"
+					d="M21 15.546c-.523 0-1.046.151-1.5.454a2.704 2.704 0 01-3 0 2.704 2.704 0 00-3 0 2.704 2.704 0 01-3 0 2.704 2.704 0 00-3 0 2.704 2.704 0 01-3 0 2.701 2.701 0 00-1.5-.454M9 6v2m3-2v2m3-2v2M9 3h.01M12 3h.01M15 3h.01M21 21v-7a2 2 0 00-2-2H5a2 2 0 00-2 2v7h18zm-3-9v-2a2 2 0 00-2-2H8a2 2 0 00-2 2v2h12z"
+				/>
+			</svg>
+		{/snippet}
+		<SettingsCard>
+			<div class="p-5 space-y-4">
+				<div class="setting-item">
+					<label class="toggle-setting">
+						<input
+							type="checkbox"
+							checked={settingsStore.showBirthdays}
+							onchange={() => settingsStore.set('showBirthdays', !settingsStore.showBirthdays)}
+						/>
+						<div class="toggle-info">
+							<span class="setting-label">Geburtstage anzeigen</span>
+							<span class="setting-description">Geburtstage aus Kontakten im Kalender anzeigen</span
+							>
+						</div>
+					</label>
+				</div>
+
+				{#if settingsStore.showBirthdays}
+					<div class="setting-item birthday-age-setting">
+						<label class="toggle-setting">
+							<input
+								type="checkbox"
+								checked={settingsStore.showBirthdayAge}
+								onchange={() =>
+									settingsStore.set('showBirthdayAge', !settingsStore.showBirthdayAge)}
+							/>
+							<div class="toggle-info">
+								<span class="setting-label">Alter anzeigen</span>
+								<span class="setting-description"
+									>Das Alter der Person bei Geburtstagen anzeigen</span
+								>
+							</div>
+						</label>
+					</div>
+				{/if}
+			</div>
+		</SettingsCard>
+	</SettingsSection>
+
 	<!-- Konto -->
 	<SettingsSection title="Konto">
 		{#snippet icon()}
@@ -643,24 +716,6 @@
 		color: hsl(var(--color-muted-foreground));
 	}
 
-	/* Select input */
-	.select-input {
-		width: 100%;
-		max-width: 250px;
-		padding: 0.5rem 0.75rem;
-		border: 2px solid hsl(var(--color-border));
-		border-radius: var(--radius-md);
-		background: hsl(var(--color-background));
-		color: hsl(var(--color-foreground));
-		font-size: 0.875rem;
-		cursor: pointer;
-	}
-
-	.select-input:focus {
-		outline: none;
-		border-color: hsl(var(--color-primary));
-	}
-
 	/* Button group */
 	.button-group {
 		display: flex;
@@ -745,15 +800,11 @@
 		gap: 0.25rem;
 	}
 
-	.hour-input-group label {
+	.hour-label {
 		font-size: 0.75rem;
 		color: hsl(var(--color-muted-foreground));
 	}
 
-	.hour-select {
-		width: 100px;
-	}
-
 	.hour-separator {
 		font-size: 1.25rem;
 		color: hsl(var(--color-muted-foreground));
@@ -1015,4 +1066,11 @@
 		padding: 1.5rem;
 		color: hsl(var(--color-muted-foreground));
 	}
+
+	/* Birthday age setting (indented sub-setting) */
+	.birthday-age-setting {
+		padding-left: 2rem;
+		border-left: 2px solid hsl(var(--color-primary) / 0.3);
+		margin-left: 0.5rem;
+	}
 </style>

apps/contacts/apps/backend/src/contact/contact.controller.ts

@@ -234,6 +234,16 @@ export class ContactController {
 		return { contacts, total };
 	}
 
+	/**
+	 * Get all contacts with birthdays (for calendar integration)
+	 * Returns lightweight data: id, displayName, firstName, lastName, birthday, photoUrl
+	 */
+	@Get('birthdays')
+	async getBirthdays(@CurrentUser() user: CurrentUserData) {
+		const contacts = await this.contactService.findWithBirthdays(user.userId);
+		return { contacts };
+	}
+
 	@Get(':id')
 	async findOne(@CurrentUser() user: CurrentUserData, @Param('id', ParseUUIDPipe) id: string) {
 		const contact = await this.contactService.findById(id, user.userId);

apps/contacts/apps/backend/src/contact/contact.service.ts

@@ -1,10 +1,19 @@
 import { Injectable, Inject, NotFoundException } from '@nestjs/common';
-import { eq, and, or, ilike, desc, sql } from 'drizzle-orm';
+import { eq, and, or, ilike, desc, sql, isNotNull } from 'drizzle-orm';
 import { DATABASE_CONNECTION } from '../db/database.module';
 import { Database } from '../db/connection';
 import { contacts } from '../db/schema';
 import type { Contact, NewContact } from '../db/schema';
 
+export interface ContactBirthdaySummary {
+	id: string;
+	displayName: string | null;
+	firstName: string | null;
+	lastName: string | null;
+	birthday: string;
+	photoUrl: string | null;
+}
+
 export interface ContactFilters {
 	search?: string;
 	isFavorite?: boolean;
@@ -148,4 +157,34 @@ export class ContactService {
 
 		return Number(result[0]?.count || 0);
 	}
+
+	/**
+	 * Find all contacts with birthdays (for calendar integration)
+	 * Returns only essential fields for lightweight transfer
+	 */
+	async findWithBirthdays(userId: string): Promise<ContactBirthdaySummary[]> {
+		const result = await this.db
+			.select({
+				id: contacts.id,
+				displayName: contacts.displayName,
+				firstName: contacts.firstName,
+				lastName: contacts.lastName,
+				birthday: contacts.birthday,
+				photoUrl: contacts.photoUrl,
+			})
+			.from(contacts)
+			.where(
+				and(
+					eq(contacts.userId, userId),
+					eq(contacts.isArchived, false),
+					isNotNull(contacts.birthday)
+				)
+			)
+			.orderBy(contacts.lastName, contacts.firstName);
+
+		return result.map((c) => ({
+			...c,
+			birthday: c.birthday || '',
+		}));
+	}
 }

scripts/generate-env.mjs

@@ -428,6 +428,9 @@ const APP_CONFIGS = [
 			PUBLIC_MANA_CORE_AUTH_URL: (env) => env.MANA_CORE_AUTH_URL,
 			PUBLIC_TODO_BACKEND_URL: (env) =>
 				env.TODO_BACKEND_URL || `http://localhost:${env.TODO_BACKEND_PORT || '3018'}`,
+			// Cross-app integration: Contacts service for birthdays
+			PUBLIC_CONTACTS_API_URL: (env) => `http://localhost:${env.CONTACTS_BACKEND_PORT || '3015'}`,
+			PUBLIC_CONTACTS_WEB_URL: () => 'http://localhost:5184',
 		},
 	},