fix(flutter): 吸顶分类行背景常驻清除闪动

test/discover/home_all_dramas_grid_test.dart

@@ -215,7 +215,7 @@ void main() {
     final before = tester.getRect(
       find.byKey(const Key('theater-sticky-header')),
     );
-    expect(header().color, Colors.transparent);
+    expect(header().color, AppColors.ink);
 
     await tester.drag(_verticalFeed, const Offset(0, -220));
     await tester.pumpAndSettle();
@@ -227,6 +227,15 @@ void main() {
     expect(header().color, AppColors.ink);
   });
 
+  testWidgets('should_paint_theater_surface_with_ink', (tester) async {
+    await _pumpTheater(tester, categoryRepository: _GridCategoryRepository());
+    final surface = tester.widget<ColoredBox>(
+      find.byKey(const Key('theater-page-surface')),
+    );
+
+    expect(surface.color, AppColors.ink);
+  });
+
   testWidgets('should_keep_category_row_stable_across_scrolls', (tester) async {
     await _pumpTheater(
       tester,