fix(flutter): 修复剧场吸顶分类行闪烁并压缩间距

lib/pages/discover/discover_view.dart

@@ -60,7 +60,7 @@ class DiscoverPage extends StatefulWidget {
 
 class _DiscoverPageState extends State<DiscoverPage> {
   late final DiscoverLogic logic;
-  bool _headerScrolled = false;
+  final ValueNotifier<bool> _headerPinned = ValueNotifier<bool>(false);
 
   bool get embedded => widget.callbacks.embedded;
 
@@ -73,10 +73,8 @@ class _DiscoverPageState extends State<DiscoverPage> {
   }
 
   void _onScroll() {
-    final scrolled = logic.scroll.hasClients && logic.scroll.offset > 0;
-    if (scrolled != _headerScrolled) {
-      setState(() => _headerScrolled = scrolled);
-    }
+    final pinned = logic.scroll.hasClients && logic.scroll.offset > 0;
+    if (pinned != _headerPinned.value) _headerPinned.value = pinned;
   }
 
   void _focusOnFirstFrame() {
@@ -99,6 +97,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
   @override
   void dispose() {
     logic.scroll.removeListener(_onScroll);
+    _headerPinned.dispose();
     logic.dispose();
     super.dispose();
   }
@@ -184,28 +183,36 @@ class _DiscoverPageState extends State<DiscoverPage> {
   }
 
   Widget _stickyHeader(AppLocalizations l10n, CategoryController categories) {
-    return AnimatedContainer(
-      key: const Key('theater-sticky-header'),
-      duration: _stickyHeaderTransition,
-      curve: Curves.easeOut,
-      decoration: BoxDecoration(
-        color: _headerScrolled ? AppColors.ink : Colors.transparent,
-        border: Border(
-          bottom: BorderSide(
-            color: _headerScrolled ? AppColors.border : Colors.transparent,
+    // 只有背景随吸顶状态变化，分类行内容（child）不参与重建，避免上滑闪烁。
+    return ValueListenableBuilder<bool>(
+      valueListenable: _headerPinned,
+      builder: (context, pinned, child) => AnimatedContainer(
+        key: const Key('theater-sticky-header'),
+        duration: _stickyHeaderTransition,
+        curve: Curves.easeOut,
+        decoration: BoxDecoration(
+          color: pinned ? AppColors.ink : Colors.transparent,
+          border: Border(
+            bottom: BorderSide(
+              color: pinned ? AppColors.border : Colors.transparent,
+            ),
           ),
+          boxShadow: pinned
+              ? const [
+                  BoxShadow(
+                    color: Color(0x14000000),
+                    blurRadius: 8,
+                    offset: Offset(0, 2),
+                  ),
+                ]
+              : const [],
         ),
-        boxShadow: _headerScrolled
-            ? const [
-                BoxShadow(
-                  color: Color(0x14000000),
-                  blurRadius: 8,
-                  offset: Offset(0, 2),
-                ),
-              ]
-            : const [],
+        child: child,
+      ),
+      child: KeyedSubtree(
+        key: const Key('theater-sticky-content'),
+        child: _categoryTabs(l10n, categories),
       ),
-      child: _categoryTabs(l10n, categories),
     );
   }
 
@@ -341,7 +348,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
 
   Widget _toolbar(AppLocalizations l10n, CategoryController categories) {
     return Padding(
-      padding: const EdgeInsets.fromLTRB(14, 10, 14, 12),
+      padding: const EdgeInsets.fromLTRB(14, 2, 14, 12),
       child: Row(
         children: [
           Expanded(