feat(flutter): 统一空列表占位组件

test/download/downloads_page_test.dart

@@ -11,6 +11,7 @@ import 'package:fruitshorts/core/data/services/auth_controller.dart';
 import 'package:fruitshorts/core/data/services/auth_session_store.dart';
 import 'package:fruitshorts/core/data/services/download_controller.dart';
 import 'package:fruitshorts/core/platform/haptics.dart';
+import 'package:fruitshorts/core/widgets/empty_state.dart';
 import 'package:fruitshorts/l10n/app_localizations.dart';
 import 'package:fruitshorts/pages/downloads/downloads_page.dart';
 import 'package:provider/provider.dart';
@@ -90,6 +91,7 @@ void main() {
     await _pumpPage(tester, auth: auth, controller: controller);
 
     expect(find.byKey(const Key('downloads-empty')), findsOneWidget);
+    expect(find.byType(EmptyState), findsOneWidget);
   });
 
   testWidgets('should_show_retry_when_policy_or_list_load_fails', (
@@ -163,6 +165,7 @@ void main() {
     expect(repository.clearCalls, 1);
     expect(haptics.mediumImpacts, 1);
     expect(find.byKey(const Key('downloads-empty')), findsOneWidget);
+    expect(find.byType(EmptyState), findsOneWidget);
   });
 
   testWidgets(