refactor(contacts,todo): extract shared utilities, eliminate duplication

Contacts:
- Extract getDisplayName() + getInitials() to lib/utils/contact-display.ts
  (was duplicated across 7 files)
- Export UNKNOWN_CONTACT_NAME constant

Todo:
- Extract getSubtaskProgress() to lib/utils/task-helpers.ts
  (was duplicated in TaskItem + KanbanTaskCard)
- Add formatDateForInput() + dateInputToISO() to date-display.ts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/todo/apps/web/src/lib/components/TaskItem.svelte

@@ -9,8 +9,10 @@
 	} from '@todo/shared';
 	import type { ContactReference, ContactOrManual } from '@manacore/shared-types';
 	import { STATUS_OPTIONS, RECURRENCE_OPTIONS } from '@todo/shared';
-	import { isToday, isPast } from 'date-fns';
+	import { format, isToday, isPast } from 'date-fns';
+	import { de } from 'date-fns/locale';
 	import { formatDueDate } from '$lib/utils/date-display';
+	import { getSubtaskProgress } from '$lib/utils/task-helpers';
 	import { getContext } from 'svelte';
 	import type { Project } from '@todo/shared';
 	import { getActiveProjects, getProjectColor } from '$lib/data/task-queries';
@@ -314,11 +316,7 @@
 	});
 
 	// Subtasks progress
-	let subtaskProgress = $derived(() => {
-		if (!task.subtasks || task.subtasks.length === 0) return null;
-		const completed = task.subtasks.filter((s) => s.isCompleted).length;
-		return `${completed}/${task.subtasks.length}`;
-	});
+	let subtaskProgress = $derived(() => getSubtaskProgress(task.subtasks));
 
 	// Long press to expand (mobile)
 	let longPressTimer: ReturnType<typeof setTimeout> | null = null;

apps/todo/apps/web/src/lib/components/kanban/KanbanTaskCard.svelte

@@ -2,6 +2,7 @@
 	import type { Task } from '@todo/shared';
 	import { isToday, isPast } from 'date-fns';
 	import { formatDueDate } from '$lib/utils/date-display';
+	import { getSubtaskProgress } from '$lib/utils/task-helpers';
 	import { ConfirmationModal, ContactAvatar } from '@manacore/shared-ui';
 	import TaskEditModal from '../TaskEditModal.svelte';
 	import {
@@ -53,11 +54,7 @@
 	});
 
 	// Subtasks progress
-	let subtaskProgress = $derived(() => {
-		if (!task.subtasks || task.subtasks.length === 0) return null;
-		const completed = task.subtasks.filter((s) => s.isCompleted).length;
-		return `${completed}/${task.subtasks.length}`;
-	});
+	let subtaskProgress = $derived(() => getSubtaskProgress(task.subtasks));
 
 	// Click to open modal
 	function handleCardClick(e: MouseEvent) {

apps/todo/apps/web/src/lib/utils/date-display.ts

@@ -10,3 +10,20 @@ export function formatDueDate(date: Date): string {
 	if (isTomorrow(date)) return 'Morgen';
 	return format(date, 'dd. MMM', { locale: de });
 }
+
+/**
+ * Format a date string for use in an HTML date input (yyyy-MM-dd).
+ * Returns empty string if no date is provided.
+ */
+export function formatDateForInput(dateString?: string | null): string {
+	if (!dateString) return '';
+	return format(new Date(dateString), 'yyyy-MM-dd');
+}
+
+/**
+ * Convert an HTML date input value (yyyy-MM-dd) to an ISO string.
+ * Returns null if the input is empty.
+ */
+export function dateInputToISO(dateString: string): string | null {
+	return dateString ? new Date(dateString).toISOString() : null;
+}

apps/todo/apps/web/src/lib/utils/task-helpers.ts

@@ -0,0 +1,9 @@
+/**
+ * Calculate subtask progress as a string like "2/5".
+ * Returns null if there are no subtasks.
+ */
+export function getSubtaskProgress(subtasks?: { isCompleted: boolean }[]): string | null {
+	if (!subtasks || subtasks.length === 0) return null;
+	const completed = subtasks.filter((s) => s.isCompleted).length;
+	return `${completed}/${subtasks.length}`;
+}