refactor(empty-state): 空状态支持内容居中

lib/pages/discover/discover_view.dart

@@ -297,6 +297,7 @@ class _DiscoverPageState extends State<DiscoverPage> {
               icon: Icons.movie_filter_outlined,
               title: l10n.noStories,
               subtitle: l10n.emptyHint,
+              stretchContent: true,
             ),
           ),
         )