feat(flutter): 首页频道行滚动吸顶

test/home/k28_a_navigation_test.dart

@@ -90,16 +90,33 @@ void main() {
     );
     expect(card.borderRadius, BorderRadius.zero);
 
-    // 频道行在 hero Stack 内、位于轮播顶部 8 的位置上。
+    // 频道行是固定层，不在可滚动列表里，初始仍压在轮播顶部。
     expect(
       find.ancestor(
         of: find.byKey(const Key('home-channels')),
-        matching: find.byKey(const Key('home-hero-section')),
+        matching: find.byKey(const Key('home-browse-page')),
       ),
-      findsOneWidget,
+      findsNothing,
     );
     final channels = tester.getRect(find.byKey(const Key('home-channels')));
-    expect(channels.top, closeTo(hero.top + 8, 1));
+    expect(channels.top, closeTo(hero.top, 1));
+    expect(find.byKey(const Key('home-channels-pinned')), findsNothing);
+  });
+
+  testWidgets('should_pin_home_channels_when_scrolling', (tester) async {
+    await _pumpApp(tester);
+    final before = tester.getRect(find.byKey(const Key('home-channel-hot')));
+    expect(find.byKey(const Key('home-channels-pinned')), findsNothing);
+
+    await tester.drag(
+      find.byKey(const Key('home-browse-page')),
+      const Offset(0, -300),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.byKey(const Key('home-channels-pinned')), findsOneWidget);
+    final after = tester.getRect(find.byKey(const Key('home-channel-hot')));
+    expect(after.top, closeTo(before.top, 0.5));
   });
 
   testWidgets('should_open_theater_search_when_home_search_is_tapped', (