refactor: keep only dashboard sidebars and their state

src/app/dashboard/page.tsx

@@ -1,13 +1,12 @@
 import { Suspense } from "react";
-import { Brand } from "@/components/brand";
 import Dashboard from "./dashboard";
 
 export default function DashboardPage() {
   return (
     <Suspense fallback={
-      <div className="loading-page">
-        <Brand />
-        <p>正在打开你的创作空间…</p>
+      <div className="dashboard sidebar-only" aria-label="正在加载侧边栏" aria-busy="true">
+        <aside className="icon-rail" />
+        <aside className="workspace-sidebar" />
       </div>
     }>
       <Dashboard />