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

@@ -186,26 +186,41 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
   }) {
     return _filterRow(
       row: row,
-      child: SingleChildScrollView(
-        key: Key('all-filter-scroll-$row'),
+      child: _horizontalChipScroll(
+        scrollKey: Key('all-filter-scroll-$row'),
+        chips: [
+          for (var index = 0; index < options.length; index++) ...[
+            _chip(
+              key: Key('all-filter-${options[index].id}'),
+              label: options[index].label,
+              selected: selected == options[index].id,
+              onTap: () => onSelected(options[index].id),
+            ),
+            if (index < options.length - 1)
+              const SizedBox(width: AppDimens.filterItemGap),
+          ],
+        ],
+      ),
+    );
+  }
+
+  Widget _horizontalChipScroll({
+    required Key scrollKey,
+    required List<Widget> chips,
+  }) {
+    return LayoutBuilder(
+      builder: (context, constraints) => SingleChildScrollView(
+        key: scrollKey,
         scrollDirection: Axis.horizontal,
         physics: const BouncingScrollPhysics(),
-        child: Row(
-          mainAxisSize: MainAxisSize.min,
-          mainAxisAlignment: MainAxisAlignment.start,
-          crossAxisAlignment: CrossAxisAlignment.center,
-          children: [
-            for (var index = 0; index < options.length; index++) ...[
-              _chip(
-                key: Key('all-filter-${options[index].id}'),
-                label: options[index].label,
-                selected: selected == options[index].id,
-                onTap: () => onSelected(options[index].id),
-              ),
-              if (index < options.length - 1)
-                const SizedBox(width: AppDimens.filterItemGap),
-            ],
-          ],
+        child: ConstrainedBox(
+          constraints: BoxConstraints(minWidth: constraints.maxWidth),
+          child: Row(
+            mainAxisSize: MainAxisSize.min,
+            mainAxisAlignment: MainAxisAlignment.start,
+            crossAxisAlignment: CrossAxisAlignment.center,
+            children: chips,
+          ),
         ),
       ),
     );
@@ -286,30 +301,23 @@ class _AllDramasFilterGridState extends State<AllDramasFilterGrid> {
         crossAxisAlignment: CrossAxisAlignment.center,
         children: [
           Expanded(
-            child: SingleChildScrollView(
-              key: const Key('all-filter-scroll-3'),
-              scrollDirection: Axis.horizontal,
-              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,
-                    selected: !_newest,
-                    onTap: () => setState(() => _newest = false),
-                  ),
-                  const SizedBox(width: AppDimens.filterItemGap),
-                  _chip(
-                    key: const Key('all-sort-new'),
-                    label: l10n.newest,
-                    selected: _newest,
-                    onTap: () => setState(() => _newest = true),
-                  ),
-                ],
-              ),
+            child: _horizontalChipScroll(
+              scrollKey: const Key('all-filter-scroll-3'),
+              chips: [
+                _chip(
+                  key: const Key('all-sort-hot'),
+                  label: l10n.hot,
+                  selected: !_newest,
+                  onTap: () => setState(() => _newest = false),
+                ),
+                const SizedBox(width: AppDimens.filterItemGap),
+                _chip(
+                  key: const Key('all-sort-new'),
+                  label: l10n.newest,
+                  selected: _newest,
+                  onTap: () => setState(() => _newest = true),
+                ),
+              ],
             ),
           ),
           const SizedBox(width: AppDimens.filterItemGap),