✨ 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/i18n/locales/de.json

@@ -2514,7 +2514,22 @@
       "visibleSuccess": "Fotos jetzt für Gäste sichtbar",
       "processingStatus": "Wird verarbeitet…",
       "processingFailed": "Fehlgeschlagen",
-      "retryQueued": "Wiederholung in Warteschlange"
+      "retryQueued": "Wiederholung in Warteschlange",
+      "viewMode": "Ansicht",
+      "gridView": "Rasteransicht",
+      "listView": "Listenansicht",
+      "columns": {
+        "photo": "Foto",
+        "category": "Kategorie",
+        "uploaded": "Hochgeladen",
+        "engagement": "Aktivität",
+        "feedback": "Feedback",
+        "size": "Größe",
+        "actions": "Aktionen",
+        "views": "Aufrufe",
+        "downloads": "Downloads",
+        "likes": "Likes"
+      }
     },
     "events": {
       "tabs": {

frontend/src/i18n/locales/en.json

@@ -2101,7 +2101,22 @@
       "visibleSuccess": "Photos now visible to guests",
       "processingStatus": "Processing…",
       "processingFailed": "Failed",
-      "retryQueued": "Retry queued"
+      "retryQueued": "Retry queued",
+      "viewMode": "View mode",
+      "gridView": "Grid view",
+      "listView": "List view",
+      "columns": {
+        "photo": "Photo",
+        "category": "Category",
+        "uploaded": "Uploaded",
+        "engagement": "Engagement",
+        "feedback": "Feedback",
+        "size": "Size",
+        "actions": "Actions",
+        "views": "Views",
+        "downloads": "Downloads",
+        "likes": "Likes"
+      }
     },
     "events": {
       "tabs": {