feat(mobile): UI-01 album cards, photo grid and full viewer

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

apps/mobile/lib/features/albums/models.dart

@@ -257,6 +257,7 @@ class Album extends AlbumSummary {
     required super.createdAt,
     required super.updatedAt,
     required super.statsSyncedAt,
+    super.cover,
   });
 
   factory Album.fromJson(Map<String, dynamic> json) => Album(
@@ -265,6 +266,9 @@ class Album extends AlbumSummary {
               (dynamic e) => Category.fromJson(e as Map<String, dynamic>),
             )
             .toList(),
+        cover: json['cover'] == null
+            ? null
+            : SignedUrl.fromJson(json['cover'] as Map<String, dynamic>),
         id: json['id'] as String,
         publicToken: json['publicToken'] as String,
         ownerId: json['ownerId'] as String,