feat(02-02): create room providers, form screen, icon picker, and router routes

- Add Riverpod providers (roomWithStatsList, RoomActions) connecting to RoomsDao
- Create RoomFormScreen with name field, icon picker preview, create/edit modes
- Create IconPickerSheet bottom sheet with curated Material Icons grid
- Add nested GoRouter routes: /rooms/new, /rooms/:roomId, /rooms/:roomId/edit
- Add placeholder TaskListScreen and TaskFormScreen for Plan 03 routes
- Add 11 new German localization keys for room management UI
- Add flutter_reorderable_grid_view dependency

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

lib/features/rooms/presentation/room_providers.dart

@@ -0,0 +1,48 @@
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+import 'package:household_keeper/core/database/database.dart';
+import 'package:household_keeper/core/providers/database_provider.dart';
+import 'package:household_keeper/features/rooms/data/rooms_dao.dart';
+
+part 'room_providers.g.dart';
+
+/// Watches all rooms with computed task stats (due count, cleanliness ratio).
+@riverpod
+Stream<List<RoomWithStats>> roomWithStatsList(Ref ref) {
+  final db = ref.watch(appDatabaseProvider);
+  return db.roomsDao.watchRoomWithStats();
+}
+
+/// Async notifier for room mutation actions (create, update, delete, reorder).
+@riverpod
+class RoomActions extends _$RoomActions {
+  @override
+  FutureOr<void> build() {}
+
+  /// Create a new room. Returns the auto-generated id.
+  Future<int> createRoom(String name, String iconName) async {
+    final db = ref.read(appDatabaseProvider);
+    return db.roomsDao.insertRoom(RoomsCompanion.insert(
+      name: name,
+      iconName: iconName,
+    ));
+  }
+
+  /// Update an existing room.
+  Future<void> updateRoom(Room room) async {
+    final db = ref.read(appDatabaseProvider);
+    await db.roomsDao.updateRoom(room);
+  }
+
+  /// Delete a room and cascade to its tasks and completions.
+  Future<void> deleteRoom(int roomId) async {
+    final db = ref.read(appDatabaseProvider);
+    await db.roomsDao.deleteRoom(roomId);
+  }
+
+  /// Reorder rooms by their IDs in the new order.
+  Future<void> reorderRooms(List<int> roomIds) async {
+    final db = ref.read(appDatabaseProvider);
+    await db.roomsDao.reorderRooms(roomIds);
+  }
+}