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/l10n/app_localizations.dart

@@ -207,6 +207,72 @@ abstract class AppLocalizations {
   /// In de, this message translates to:
   /// **'Version {version}'**
   String aboutVersion(String version);
+
+  /// No description provided for @roomFormCreateTitle.
+  ///
+  /// In de, this message translates to:
+  /// **'Raum erstellen'**
+  String get roomFormCreateTitle;
+
+  /// No description provided for @roomFormEditTitle.
+  ///
+  /// In de, this message translates to:
+  /// **'Raum bearbeiten'**
+  String get roomFormEditTitle;
+
+  /// No description provided for @roomFormNameLabel.
+  ///
+  /// In de, this message translates to:
+  /// **'Raumname'**
+  String get roomFormNameLabel;
+
+  /// No description provided for @roomFormNameHint.
+  ///
+  /// In de, this message translates to:
+  /// **'z.B. Küche, Badezimmer...'**
+  String get roomFormNameHint;
+
+  /// No description provided for @roomFormNameRequired.
+  ///
+  /// In de, this message translates to:
+  /// **'Bitte einen Namen eingeben'**
+  String get roomFormNameRequired;
+
+  /// No description provided for @roomFormIconLabel.
+  ///
+  /// In de, this message translates to:
+  /// **'Symbol wählen'**
+  String get roomFormIconLabel;
+
+  /// No description provided for @roomDeleteConfirmTitle.
+  ///
+  /// In de, this message translates to:
+  /// **'Raum löschen?'**
+  String get roomDeleteConfirmTitle;
+
+  /// No description provided for @roomDeleteConfirmMessage.
+  ///
+  /// In de, this message translates to:
+  /// **'Der Raum und alle zugehörigen Aufgaben werden unwiderruflich gelöscht.'**
+  String get roomDeleteConfirmMessage;
+
+  /// No description provided for @roomDeleteConfirmAction.
+  ///
+  /// In de, this message translates to:
+  /// **'Löschen'**
+  String get roomDeleteConfirmAction;
+
+  /// No description provided for @roomCardDueCount.
+  ///
+  /// In de, this message translates to:
+  /// **'{count} fällig'**
+  String roomCardDueCount(int count);
+
+  /// No description provided for @cancel.
+  ///
+  /// In de, this message translates to:
+  /// **'Abbrechen'**
+  String get cancel;
 }
 
 class _AppLocalizationsDelegate