fix(frontend): 聊天页单屏布局并消除 F5 滚底闪烁

锁定视口避免双滚动；消息列表改用 flex-col-reverse，SSR/无 JS 默认贴最新消息。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/chat/page.tsx

@@ -27,8 +27,6 @@ export default async function ChatListPage() {
   }
 
   return (
-    <div className="max-w-6xl mx-auto">
-      <ChatShell meId={me.user.id} initialRooms={rooms} activeRoomId={null} />
-    </div>
+    <ChatShell meId={me.user.id} initialRooms={rooms} activeRoomId={null} />
   );
 }