refactor(date): consolidate formatDate in date.ts with optional format param

Add format?: 'short'|'long' (default 'long') to date.ts formatDate and
remove the duplicate from personFormat.ts. Update DocumentTopBar to
import from date.ts directly. Move the formatDate tests from
personFormat.spec to date.spec.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/DocumentTopBar.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
 import { slide } from 'svelte/transition';
-import { formatDate } from '$lib/utils/personFormat';
+import { formatDate } from '$lib/utils/date';
 import { clickOutside } from '$lib/actions/clickOutside';
 import PersonChipRow from './PersonChipRow.svelte';
 import OverflowPillButton from './OverflowPillButton.svelte';

frontend/src/lib/utils/date.spec.ts

@@ -1,5 +1,25 @@
 import { describe, expect, it } from 'vitest';
-import { formatGermanDateInput, isoToGerman, germanToIso } from './date';
+import { formatDate, formatGermanDateInput, isoToGerman, germanToIso } from './date';
+
+// ─── formatDate ──────────────────────────────────────────────────────────────
+
+describe('formatDate', () => {
+	it('defaults to long format when no format arg is passed', () => {
+		expect(formatDate('1943-12-24')).toBe('24. Dezember 1943');
+	});
+
+	it('formats long date with German month name', () => {
+		expect(formatDate('1943-12-24', 'long')).toBe('24. Dezember 1943');
+	});
+
+	it('formats short date as dd.mm.yyyy', () => {
+		expect(formatDate('1943-12-24', 'short')).toBe('24.12.1943');
+	});
+
+	it('does not shift Dec 31 to Jan 1 (T12:00:00 UTC guard)', () => {
+		expect(formatDate('1943-12-31', 'short')).toBe('31.12.1943');
+	});
+});
 
 // ─── isoToGerman ─────────────────────────────────────────────────────────────
 

frontend/src/lib/utils/date.ts

@@ -1,13 +1,22 @@
 /**
  * Format an ISO date string (YYYY-MM-DD) for display.
  * Uses T12:00:00 to avoid UTC timezone off-by-one when converting to local time.
+ * Defaults to 'long' (e.g. "24. Dezember 1943"); pass 'short' for DD.MM.YYYY.
  */
-export function formatDate(isoDate: string): string {
+export function formatDate(isoDate: string, format: 'short' | 'long' = 'long'): string {
+	const date = new Date(isoDate + 'T12:00:00');
+	if (format === 'short') {
+		return new Intl.DateTimeFormat('de-DE', {
+			day: '2-digit',
+			month: '2-digit',
+			year: 'numeric'
+		}).format(date);
+	}
 	return new Intl.DateTimeFormat('de-DE', {
 		day: 'numeric',
 		month: 'long',
 		year: 'numeric'
-	}).format(new Date(isoDate + 'T12:00:00'));
+	}).format(date);
 }
 
 /**

frontend/src/lib/utils/personFormat.spec.ts

@@ -4,10 +4,10 @@ import {
 	abbreviateName,
 	formatXsMeta,
 	personAvatarColor,
-	formatDate,
 	statusDotClass,
 	statusLabel
 } from './personFormat';
+import { formatDate } from './date';
 
 // ─── getInitials ─────────────────────────────────────────────────────────────
 

frontend/src/lib/utils/personFormat.ts

@@ -1,4 +1,5 @@
 import { formatDocumentStatus } from './documentStatusLabel';
+import { formatDate } from './date';
 
 type Person = { firstName?: string | null; lastName: string; displayName: string };
 type DocumentStatus = 'PLACEHOLDER' | 'UPLOADED' | 'TRANSCRIBED' | 'REVIEWED' | 'ARCHIVED';
@@ -75,22 +76,6 @@ export function personAvatarColor(personId: string): string {
 	return AVATAR_PALETTE[djb2(personId) % AVATAR_PALETTE.length];
 }
 
-export function formatDate(isoDate: string, format: 'short' | 'long'): string {
-	const date = new Date(isoDate + 'T12:00:00');
-	if (format === 'short') {
-		return new Intl.DateTimeFormat('de-DE', {
-			day: '2-digit',
-			month: '2-digit',
-			year: 'numeric'
-		}).format(date);
-	}
-	return new Intl.DateTimeFormat('de-DE', {
-		day: 'numeric',
-		month: 'long',
-		year: 'numeric'
-	}).format(date);
-}
-
 export function statusDotClass(status: DocumentStatus): string {
 	switch (status) {
 		case 'PLACEHOLDER':