Revert "merge: 合并 K95.2 首切频道封面过渡"

This reverts commit a2a491d056, reversing
changes made to 838ca2ce2a.

test/player/player_fullscreen_test.dart

@@ -131,12 +131,18 @@ void main() {
     expect(player.playing, isTrue);
   });
 
-  testWidgets('should_show_poster_before_video_first_frame', (tester) async {
+  testWidgets('should_keep_video_surface_background_black', (tester) async {
     await _pumpApp(tester);
     await _openSeriesPlayer(tester);
 
-    expect(find.byKey(const Key('player-video-poster')), findsOneWidget);
-    expect(find.byKey(const Key('player-fallback-background')), findsNothing);
+    expect(
+      tester
+          .widget<ColoredBox>(
+            find.byKey(const Key('player-fallback-background')),
+          )
+          .color,
+      Colors.black,
+    );
     expect(find.byKey(const Key('player-fallback-cover')), findsNothing);
     expect(find.byKey(const Key('player-fallback-scrim')), findsNothing);
   });
@@ -465,8 +471,9 @@ void main() {
       find.byKey(const Key('player-interaction-rail')),
     );
     expect(find.byKey(const Key('player-background')), findsNothing);
-    expect(find.byKey(const Key('player-video-poster')), findsOneWidget);
-    expect(find.byKey(const Key('player-fallback-background')), findsNothing);
+    final fallback = find.byKey(const Key('player-fallback-background'));
+    expect(fallback, findsOneWidget);
+    expect(tester.widget<ColoredBox>(fallback).color, Colors.black);
     expect(find.byKey(const Key('player-fallback-cover')), findsNothing);
     expect(find.byKey(const Key('player-fallback-scrim')), findsNothing);
     expect(