Stabilize auth flow and profile images

app/test/favorites/favorites_repository_test.dart

@@ -0,0 +1,45 @@
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:tdc114plus/src/features/favorites/data/favorites_repository.dart';
+
+void main() {
+  test('loads empty favorites when storage is empty', () async {
+    final repository = SharedPreferencesFavoritesRepository.withStore(
+      _MemoryFavoritesStore(),
+    );
+
+    final favorites = await repository.loadFavorites();
+
+    expect(favorites, isEmpty);
+  });
+
+  test('toggles favorites in local storage', () async {
+    final repository = SharedPreferencesFavoritesRepository.withStore(
+      _MemoryFavoritesStore(),
+    );
+
+    await repository.toggleFavorite('user-001');
+    final added = await repository.loadFavorites();
+
+    expect(added.map((favorite) => favorite.employeeId), ['user-001']);
+
+    await repository.toggleFavorite('user-001');
+    final removed = await repository.loadFavorites();
+
+    expect(removed, isEmpty);
+  });
+}
+
+class _MemoryFavoritesStore implements FavoritesKeyValueStore {
+  final _values = <String, String>{};
+
+  @override
+  Future<String?> getString(String key) async {
+    return _values[key];
+  }
+
+  @override
+  Future<void> setString(String key, String value) async {
+    _values[key] = value;
+  }
+}