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/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 || '',
+		}));
+	}
 }