fix(player): 修复清晰度切换闪屏与还原黑屏

lib/core/data/services/playback_session.dart

@@ -11,7 +11,7 @@ part 'playback_neighbors.dart';
 part 'playback_session_controls.dart';
 
 /// 新纹理第一帧常是黑的，旧画面只盖住这一小段。
-const Duration _qualityHandoffHold = Duration(milliseconds: 200);
+const Duration _qualityHandoffHold = Duration(milliseconds: 500);
 
 typedef PlayerFactory = PlayerPort Function(Episode episode);
 typedef PlayerPreparation =

lib/core/data/services/watch_records_controller.dart

@@ -144,6 +144,14 @@ class WatchRecordsController extends ChangeNotifier {
     return _detailCache[dramaId];
   }
 
+  /// 按剧集 id 找最近观看记录，供收藏网格显示「看到第n集」与继续观看横幅。
+  WatchRecord? recordForDrama(String dramaId) {
+    for (final record in records) {
+      if (record.dramaId == dramaId) return record;
+    }
+    return null;
+  }
+
   /// 删除单条记录，先更新 UI，失败按原位置回滚。
   Future<bool> remove(String dramaId) async {
     final index = _recordIndex(dramaId);