feat(home): 首页改为三列探索网格

test/home/home_startup_splash_test.dart

@@ -123,7 +123,7 @@ void main() {
     await tester.pumpAndSettle();
 
     expect(find.byKey(const Key('startup-splash')), findsNothing);
-    expect(find.byKey(const Key('home-feed-title')), findsOneWidget);
+    expect(find.byKey(const Key('home-grid')), findsOneWidget);
   });
 }