fix(player): 优化封面过渡与换集起播

lib/pages/player/widgets/player_video_surface.dart

@@ -64,9 +64,12 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
           key: Key('player-fallback-background'),
           color: AppColors.mediaBlack,
         ),
-        if (!reveal && widget.openingFrame != null)
-          KeyedSubtree(
+        if (widget.openingFrame != null)
+          AnimatedOpacity(
             key: const Key('player-opening-frame'),
+            opacity: reveal ? 0 : 1,
+            duration: handoff != null ? Duration.zero : _videoFadeDuration,
+            curve: Curves.easeOut,
             child: widget.openingFrame!,
           ),
         AnimatedOpacity(