fix(flutter): 优化播放加载占位与主题色

test/player/player_fullscreen_test.dart

@@ -49,6 +49,26 @@ void main() {
     expect(tester.takeException(), isNull);
   });
 
+  testWidgets('should_fall_back_to_black_when_poster_is_empty', (tester) async {
+    await _pumpApp(
+      tester,
+      catalog: FakeCatalogRepository(dramas: const [_noCoverDrama]),
+    );
+    await _openSeriesPlayer(
+      tester,
+      cardKey: const Key('home-drama-card-no-cover-demo'),
+    );
+
+    expect(
+      tester
+          .widget<ColoredBox>(
+            find.byKey(const Key('player-fallback-background')),
+          )
+          .color,
+      Colors.black,
+    );
+  });
+
   testWidgets('should_show_center_toggle_only_when_paused', (tester) async {
     await _pumpApp(tester);
     await _openSeriesPlayer(tester);
@@ -283,9 +303,14 @@ void main() {
     );
     expect(find.byKey(const Key('player-background')), findsNothing);
     final fallback = find.byKey(const Key('player-fallback-background'));
-    if (fallback.evaluate().isNotEmpty) {
-      expect(tester.widget<ColoredBox>(fallback).color, Colors.black);
-    }
+    expect(fallback, findsOneWidget);
+    expect(find.byKey(const Key('player-fallback-cover')), findsOneWidget);
+    expect(
+      tester
+          .widget<ColoredBox>(find.byKey(const Key('player-fallback-scrim')))
+          .color,
+      const Color(0x66000000),
+    );
     expect(
       tester
           .widget<Scaffold>(find.byKey(const Key('player-scaffold')))
@@ -1024,3 +1049,20 @@ const _lockedDrama = Drama(
     ),
   ],
 );
+
+const _noCoverDrama = Drama(
+  id: 'no-cover-demo',
+  title: 'No Cover Demo',
+  synopsis: 'No cover synopsis',
+  posterUrl: '',
+  detailLoaded: true,
+  episodes: [
+    Episode(
+      id: 'no-cover-demo-1',
+      number: 1,
+      title: 'No Cover Episode',
+      isFree: true,
+      videoUrl: 'https://example.test/no-cover-demo-1.mp4',
+    ),
+  ],
+);