fix(recommend): 修正窄筛选行横向居中

docs/plans/PROGRESS.md

@@ -1220,3 +1220,5 @@ $ flutter test
 - 第 4 行仅最热/最新在滚动区内，44 圆形筛选按钮固定在滚动区外；`flutter analyze` 无问题。
 - 四行统一复用 `_filterRow` 构建，筛选区仅保留一层左右 12 padding。
 - 新增量化测试断言四行首项 x 均为 12、相邻 chip 间距均为 10；`flutter analyze` 无问题。
+- 修复横向 viewport 对短内容居中：滚动内容最小宽度撑满视口后由 Row.start 排列。
+- `flutter test test/recommend/all_dramas_filter_alignment_test.dart`：1 项测试通过。

lib/pages/recommend/widgets/all_dramas_filter_grid.dart

@@ -186,15 +186,9 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
   }) {
     return _filterRow(
       row: row,
-      child: SingleChildScrollView(
+      child: _horizontalChipScroll(
-        key: Key('all-filter-scroll-$row'),
+        scrollKey: Key('all-filter-scroll-$row'),
-        scrollDirection: Axis.horizontal,
+        chips: [
-        physics: const BouncingScrollPhysics(),
-        child: Row(
-          mainAxisSize: MainAxisSize.min,
-          mainAxisAlignment: MainAxisAlignment.start,
-          crossAxisAlignment: CrossAxisAlignment.center,
-          children: [
           for (var index = 0; index < options.length; index++) ...[
             _chip(
               key: Key('all-filter-${options[index].id}'),
@@ -207,6 +201,27 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
           ],
         ],
       ),
+    );
+  }
+
+  Widget _horizontalChipScroll({
+    required Key scrollKey,
+    required List<Widget> chips,
+  }) {
+    return LayoutBuilder(
+      builder: (context, constraints) => SingleChildScrollView(
+        key: scrollKey,
+        scrollDirection: Axis.horizontal,
+        physics: const BouncingScrollPhysics(),
+        child: ConstrainedBox(
+          constraints: BoxConstraints(minWidth: constraints.maxWidth),
+          child: Row(
+            mainAxisSize: MainAxisSize.min,
+            mainAxisAlignment: MainAxisAlignment.start,
+            crossAxisAlignment: CrossAxisAlignment.center,
+            children: chips,
+          ),
+        ),
       ),
     );
   }
@@ -286,15 +301,9 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
         crossAxisAlignment: CrossAxisAlignment.center,
         children: [
           Expanded(
-            child: SingleChildScrollView(
+            child: _horizontalChipScroll(
-              key: const Key('all-filter-scroll-3'),
+              scrollKey: const Key('all-filter-scroll-3'),
-              scrollDirection: Axis.horizontal,
+              chips: [
-              physics: const BouncingScrollPhysics(),
-              child: Row(
-                mainAxisSize: MainAxisSize.min,
-                mainAxisAlignment: MainAxisAlignment.start,
-                crossAxisAlignment: CrossAxisAlignment.center,
-                children: [
                 _chip(
                   key: const Key('all-sort-hot'),
                   label: l10n.hot,
@@ -311,7 +320,6 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
               ],
             ),
           ),
-          ),
           const SizedBox(width: AppDimens.filterItemGap),
           Material(
             key: const Key('all-dramas-filter-page-button'),