feat(flutter): 榜单前三铺满与剧场分类吸顶下划线

lib/pages/discover/discover_view.dart

@@ -34,7 +34,7 @@ const double _categoryTabHeight = 44;
 const double _categoryTabGap = 20;
 const double _categorySelectedFontSize = 16;
 const double _categoryFontSize = 15;
-const double _stickyHeaderHeight = 102;
+const double _stickyHeaderHeight = 44;
 const Duration _stickyHeaderTransition = Duration(milliseconds: 200);
 
 /// K28-A2 剧场页：搜索、分类/语言 chips 与双列剧库。
@@ -203,10 +203,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
               ]
             : const [],
       ),
-      child: Column(
-        mainAxisSize: MainAxisSize.min,
-        children: [_categoryTabs(l10n, categories), _toolbar(l10n, categories)],
-      ),
+      child: _categoryTabs(l10n, categories),
     );
   }
 
@@ -251,6 +248,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
         ? categories.feed.dramas
         : categories.dramasOf(logic.selectedCategoryId!);
     return [
+      _toolbar(l10n, categories),
       if (dramas.isEmpty)
         Padding(
           padding: const EdgeInsets.symmetric(vertical: 40),
@@ -279,6 +277,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
           if (index == 0) {
             return _categoryTab(
               key: const Key('theater-category-all'),
+              id: 'all',
               label: l10n.all,
               selected: logic.selectedCategoryId == null,
               onTap: () => logic.selectCategory(null),
@@ -287,6 +286,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
           final category = categories.categories[index - 1];
           return _categoryTab(
             key: Key('theater-category-${category.id}'),
+            id: category.id,
             label: category.name,
             selected: logic.selectedCategoryId == category.id,
             onTap: () => logic.selectCategory(category.id),
@@ -298,6 +298,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
 
   Widget _categoryTab({
     required Key key,
+    required String id,
     required String label,
     required bool selected,
     required VoidCallback onTap,
@@ -306,16 +307,32 @@ class _DiscoverPageState extends State<DiscoverPage> {
       key: key,
       behavior: HitTestBehavior.opaque,
       onTap: onTap,
-      child: Center(
-        child: Text(
-          label,
-          maxLines: 1,
-          style: TextStyle(
-            color: selected ? AppColors.onSurface : AppColors.muted,
-            fontSize: selected ? _categorySelectedFontSize : _categoryFontSize,
-            fontWeight: selected ? FontWeight.w800 : FontWeight.w500,
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        mainAxisAlignment: MainAxisAlignment.center,
+        children: [
+          Text(
+            label,
+            maxLines: 1,
+            style: TextStyle(
+              color: selected ? AppColors.onSurface : AppColors.muted,
+              fontSize: selected
+                  ? _categorySelectedFontSize
+                  : _categoryFontSize,
+              fontWeight: selected ? FontWeight.w800 : FontWeight.w500,
+            ),
           ),
-        ),
+          const SizedBox(height: 4),
+          Container(
+            key: Key('theater-category-underline-$id'),
+            width: 18,
+            height: 2,
+            decoration: BoxDecoration(
+              color: selected ? AppColors.blue : Colors.transparent,
+              borderRadius: BorderRadius.circular(1),
+            ),
+          ),
+        ],
       ),
     );
   }