feat(flutter): 增加目录加载诊断与前台重试

lib/pages/discover/discover_view.dart

@@ -2,12 +2,14 @@
 
 import 'dart:async';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 import 'package:provider/provider.dart';
 
 import '../../core/data/models/drama.dart';
 import '../../core/data/repositories/search_repository.dart';
+import '../../core/data/services/catalog_retry.dart';
 import '../../core/data/services/category_controller.dart';
 import '../../core/formatting/error_text.dart';
 import '../../core/theme/app_colors.dart';
@@ -15,6 +17,7 @@ import '../../core/theme/app_dimens.dart';
 import '../../core/theme/app_theme.dart';
 import '../../core/widgets/app_bottom_nav.dart';
 import '../../core/widgets/app_pull_to_refresh.dart';
+import '../../core/widgets/catalog_debug_info.dart';
 import '../../core/widgets/empty_state.dart';
 import '../../l10n/app_localizations.dart';
 import '../filter/filter_page.dart';
@@ -253,7 +256,10 @@ class _DiscoverPageState extends State<DiscoverPage> {
             title: errorText(l10n, error, l10n.categoriesError),
             subtitle: l10n.emptyHint,
             actionLabel: l10n.retry,
-            onAction: categories.load,
+            onAction: () => unawaited(_retryCategories(categories)),
+            footer: kDebugMode
+                ? CatalogDebugInfo(error: categories.debugError ?? error)
+                : null,
           ),
         ),
       ];
@@ -503,8 +509,14 @@ class _DiscoverPageState extends State<DiscoverPage> {
     Navigator.of(context).push<void>(MaterialPageRoute(builder: (_) => page));
   }
 
-  Widget _block(Widget child) =>
-      SizedBox(height: 280, child: Center(child: child));
+  Widget _block(Widget child) => ConstrainedBox(
+    constraints: const BoxConstraints(minHeight: 280),
+    child: Center(child: child),
+  );
+
+  Future<void> _retryCategories(CategoryController categories) {
+    return retryCatalogLoad(reload: categories.load);
+  }
 
   void _act(DiscoverPageAction action) {
     logic.act(