feat: 增加搜索结果下拉刷新

docs/plans/PROGRESS.md

@@ -1311,3 +1311,4 @@ $ flutter test
 - 搜索页提供返回、自动聚焦输入框与取消，复用 `/app/search` 逻辑和首页三列卡片。
 - 清理旧的 searchRequest/focusSearch/syncSearch 参数；`flutter analyze`：No issues found。
 - 搜索页结果改为独立两列卡片，左右 14、列距 12、行距 16，并移除 HomeFeedCard 复用。
+- 搜索结果支持下拉刷新：保留旧结果按当前关键词重取第一页，空关键词直接回弹且不改变焦点。

lib/pages/discover/discover_logic.dart

@@ -61,6 +61,14 @@ class DiscoverLogic extends ChangeNotifier {
     if (query.isNotEmpty) unawaited(_runSearch(query));
   }
 
+  /// 用当前关键词重新请求第一页；刷新期间保留旧结果。
+  Future<void> refreshSearch() async {
+    final query = search.text.trim();
+    if (query.isEmpty) return;
+    _searchTimer?.cancel();
+    await _runSearch(query, preserveResults: true);
+  }
+
   void _resetSearch() {
     _searchTimer?.cancel();
     _searchRequest++;
@@ -85,7 +93,7 @@ class DiscoverLogic extends ChangeNotifier {
     _searchTimer = Timer(searchDebounce, () => unawaited(_runSearch(query)));
   }
 
-  Future<void> _runSearch(String query) async {
+  Future<void> _runSearch(String query, {bool preserveResults = false}) async {
     final repository = searchRepository;
     if (repository == null) return;
     final request = ++_searchRequest;
@@ -101,9 +109,17 @@ class DiscoverLogic extends ChangeNotifier {
       if (request != _searchRequest) return;
       searchResults = result.list;
     } on ApiException catch (exception) {
-      _applySearchError(request, exception.message);
+      _applySearchError(
+        request,
+        exception.message,
+        preserveResults: preserveResults,
+      );
     } catch (_) {
-      _applySearchError(request, 'searchFailed');
+      _applySearchError(
+        request,
+        'searchFailed',
+        preserveResults: preserveResults,
+      );
     } finally {
       if (request == _searchRequest) {
         searchLoading = false;
@@ -112,8 +128,13 @@ class DiscoverLogic extends ChangeNotifier {
     }
   }
 
-  void _applySearchError(int request, String message) {
+  void _applySearchError(
+    int request,
+    String message, {
+    bool preserveResults = false,
+  }) {
     if (request != _searchRequest) return;
+    if (preserveResults && searchResults.isNotEmpty) return;
     searchError = message;
     searchResults = const [];
   }

lib/pages/discover/search_page.dart

@@ -11,6 +11,7 @@ import '../../core/formatting/error_text.dart';
 import '../../core/theme/app_colors.dart';
 import '../../core/theme/app_dimens.dart';
 import '../../core/theme/app_theme.dart';
+import '../../core/widgets/app_pull_to_refresh.dart';
 import '../../core/widgets/empty_state.dart';
 import '../../l10n/app_localizations.dart';
 import '../player/open_player.dart';
@@ -64,7 +65,13 @@ class _SearchPageState extends State<SearchPage> {
             child: Column(
               children: [
                 _header(l10n),
-                Expanded(child: _body(l10n)),
+                Expanded(
+                  child: AppPullToRefresh(
+                    key: const Key('search-refresh'),
+                    onRefresh: _logic.refreshSearch,
+                    child: _body(l10n),
+                  ),
+                ),
               ],
             ),
           ),
@@ -182,15 +189,20 @@ class _SearchPageState extends State<SearchPage> {
 
   Widget _body(AppLocalizations l10n) {
     if (!_logic.hasSearchQuery) {
-      return EmptyState(
+      return _stateScroll(
+        EmptyState(
           key: const Key('search-idle'),
           icon: Icons.search_rounded,
           title: l10n.searchDiscover,
+        ),
       );
     }
+    if (_logic.searchResults.isNotEmpty) {
+      return _resultsGrid();
+    }
     if (_logic.searchLoading) {
-      return const Center(
+      return _stateScroll(
-        child: SizedBox.square(
+        const SizedBox.square(
           key: Key('search-loading'),
           dimension: 20,
           child: CircularProgressIndicator(
@@ -201,22 +213,41 @@ class _SearchPageState extends State<SearchPage> {
       );
     }
     if (_logic.searchError != null) {
-      return EmptyState(
+      return _stateScroll(
+        EmptyState(
           key: const Key('search-error'),
           icon: Icons.cloud_off_rounded,
           title: errorText(l10n, _logic.searchError, l10n.searchFailed),
           actionLabel: l10n.retry,
           onAction: _logic.retrySearch,
+        ),
       );
     }
-    if (_logic.searchResults.isEmpty) {
+    return _stateScroll(
-      return EmptyState(
+      EmptyState(
         key: const Key('search-empty'),
         icon: Icons.search_off_rounded,
         title: l10n.noSearchResults,
         subtitle: l10n.emptyHint,
+      ),
     );
   }
+
+  Widget _stateScroll(Widget child) {
+    return LayoutBuilder(
+      builder: (context, constraints) => ListView(
+        physics: AppPullToRefresh.physics,
+        children: [
+          SizedBox(
+            height: constraints.maxHeight,
+            child: Center(child: child),
+          ),
+        ],
+      ),
+    );
+  }
+
+  Widget _resultsGrid() {
     return LayoutBuilder(
       builder: (context, constraints) {
         final width =
@@ -229,6 +260,7 @@ class _SearchPageState extends State<SearchPage> {
             AppDimens.searchResultTextExtent;
         return GridView.builder(
           key: const Key('search-results-grid'),
+          physics: AppPullToRefresh.physics,
           padding: const EdgeInsets.fromLTRB(
             AppDimens.feedPageHorizontal,
             AppDimens.spaceMd,