✨ Add grid/list layout toggle to admin Photos tab

The event detail Photos tab (AdminPhotoGrid) only offered a thumbnail
grid. Add a Grid/List toggle in the action bar so admins can scan
photos in a compact, metadata-oriented list.

- New utils/photoViewPrefs.ts persists the choice per admin via
  localStorage (mirrors utils/calendarPrefs.ts), defaulting to grid
- List view is a compact <table> following the established admin
  list pattern (EventsListPage), with responsive column hiding:
  Photo (thumbnail + filename + original + Video/Hidden badges),
  Category (lg+), Uploaded date (md+, via useLocalizedDate),
  Engagement views/downloads/likes (xl+), Feedback rating/comments
  (sm+), Size, and hover Actions (download, delete)
- Rows reuse the existing selection, download, delete and category
  handlers; row click opens the photo viewer
- Toggle buttons use LayoutGrid / List icons with aria-pressed state
- Add en.json + de.json keys under admin.photos (viewMode, gridView,
  listView, columns.*)
- Tests for the persistence util and the toggle's render + persistence

frontend/src/utils/__tests__/photoViewPrefs.test.ts

@@ -0,0 +1,43 @@
+/**
+ * Coverage for the admin Photos-tab layout toggle persistence.
+ *
+ * The event detail Photos tab can render as a Grid or a List; the
+ * choice is stored per browser/admin via localStorage so it survives
+ * reloads. These tests pin the default ('grid'), the round-trip, and
+ * the defensive fallback on malformed / blocked storage so a refactor
+ * can't silently break the persisted preference.
+ */
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+import { getPhotoViewMode, setPhotoViewMode } from '../photoViewPrefs';
+
+describe('photoViewPrefs', () => {
+  beforeEach(() => {
+    localStorage.clear();
+  });
+  afterEach(() => {
+    localStorage.clear();
+  });
+
+  it('defaults to grid when nothing is stored', () => {
+    expect(getPhotoViewMode()).toBe('grid');
+  });
+
+  it('round-trips a persisted view mode', () => {
+    setPhotoViewMode('list');
+    expect(getPhotoViewMode()).toBe('list');
+    setPhotoViewMode('grid');
+    expect(getPhotoViewMode()).toBe('grid');
+  });
+
+  it('falls back to grid for an unrecognised stored value', () => {
+    localStorage.setItem('picpeak.adminPhotos.view', 'mosaic');
+    expect(getPhotoViewMode()).toBe('grid');
+  });
+
+  it('ignores attempts to persist an invalid view mode', () => {
+    setPhotoViewMode('list');
+    // @ts-expect-error — exercising the runtime guard against bad input
+    setPhotoViewMode('carousel');
+    expect(getPhotoViewMode()).toBe('list');
+  });
+});

frontend/src/utils/photoViewPrefs.ts

@@ -0,0 +1,52 @@
+/**
+ * photoViewPrefs — localStorage-backed admin photo-grid preferences.
+ *
+ * Single key today: the last-used layout for the event Photos tab
+ * (Grid or List). Stored per browser/admin pair via localStorage so the
+ * toggle persists across page reloads. No server round-trip.
+ *
+ * If more admin-tunable photo preferences land, extend this module with
+ * a JSON object keyed at `picpeak.adminPhotos.prefs` instead of more
+ * individual keys (see utils/calendarPrefs.ts for the same convention).
+ *
+ * The getter swallows malformed values (e.g. someone hand-edits the
+ * stored value) and falls back to the documented default — never
+ * throws on read.
+ */
+
+const VIEW_KEY = 'picpeak.adminPhotos.view';
+
+export type PhotoViewMode = 'grid' | 'list';
+
+const ALLOWED_VIEWS: ReadonlyArray<PhotoViewMode> = ['grid', 'list'];
+
+/**
+ * Return the persisted view or the default ('grid').
+ * Safe to call before localStorage exists (SSR / test envs).
+ */
+export function getPhotoViewMode(): PhotoViewMode {
+  if (typeof window === 'undefined' || !window.localStorage) return 'grid';
+  try {
+    const raw = window.localStorage.getItem(VIEW_KEY);
+    if (raw && (ALLOWED_VIEWS as readonly string[]).includes(raw)) {
+      return raw as PhotoViewMode;
+    }
+  } catch (_) {
+    // ignore — fall through to default
+  }
+  return 'grid';
+}
+
+/**
+ * Persist the active view. Silently no-ops when localStorage is
+ * unavailable.
+ */
+export function setPhotoViewMode(view: PhotoViewMode): void {
+  if (typeof window === 'undefined' || !window.localStorage) return;
+  if (!(ALLOWED_VIEWS as readonly string[]).includes(view)) return;
+  try {
+    window.localStorage.setItem(VIEW_KEY, view);
+  } catch (_) {
+    // ignore — quota / disabled storage
+  }
+}