fix: report group control failures

test/read_only_load_state_test.dart

@@ -478,4 +478,24 @@ void main() {
     expect(api.controlledGroupId, 'kitchen');
     expect(api.controlGroupParams, containsPair('scene', 'party'));
   });
+
+  test('debounced group control error is reported', () async {
+    final api = FakeIgnisApi();
+    final container = containerWith(api);
+    api.controlGroupError = DioException(
+      requestOptions: RequestOptions(path: '/control/group/kitchen'),
+      type: DioExceptionType.connectionError,
+      message: 'No route to host',
+    );
+
+    container.read(groupsProvider.notifier).setBrightness('kitchen', 42);
+    await Future<void>.delayed(const Duration(milliseconds: 400));
+
+    final error = container.read(groupControlErrorProvider);
+    expect(error, isNotNull);
+    expect(error!.groupId, 'kitchen');
+    expect(error.action, 'яркость');
+    expect(error.message, contains('Backend недоступен'));
+    expect(api.controlGroupParams, containsPair('brightness', 42));
+  });
 }