perf(following): 追剧页不可见时不再提前拉观看历史

首页用 IndexedStack 常驻四个 tab，追剧页一启动就会发一次观看历史请求，和首页 feed 抢网络；
改为切到该 tab 时再加载，收藏列表也只在首次可见且为空时补拉。

test/following/following_page_test.dart

@@ -23,6 +23,29 @@ import '../support/fake_interaction_repositories.dart';
 import '../support/widget_player.dart';
 
 void main() {
+  testWidgets('should_defer_watch_history_until_following_tab_is_opened', (
+    tester,
+  ) async {
+    SharedPreferencesAsyncPlatform.instance =
+        InMemorySharedPreferencesAsync.empty();
+    final catalog = FakeCatalogRepository();
+    final history = _IdentityWatchHistoryRepository(
+      device: [_historyProgress('the-signal-demo', 'Device history')],
+      account: const [],
+    );
+    await tester.pumpWidget(_app(catalog: catalog, history: history));
+    await tester.pumpAndSettle();
+
+    // 首页默认停在推荐 tab：追剧页虽在 IndexedStack 里，也不该提前拉观看历史。
+    // 启动时只有「我的」页会拉一次，追剧页若也拉就会变成 2。
+    expect(history.recentCalls, 1);
+
+    await tester.tap(find.byKey(const Key('tab-follow')));
+    await tester.pumpAndSettle();
+
+    expect(history.recentCalls, greaterThan(0));
+  });
+
   testWidgets('should_render_following_tabs_grid_and_edit_actions', (
     tester,
   ) async {