frontend: rebuild bookmark page with drag-and-drop, search, and theme system

- bookmark management with dnd-kit reordering, bulk edit, search,
  category filter/rename, and meta auto-fetch
- migrate /bookmarks → /dashboard/bookmarks under (main) layout
- homepage redesign with category grid, /-key search, dock tooltips
- theme toggle + use-theme, sonner toasts, alert-dialog/skeleton,
  visual refresh of auth pages

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/app/bind-account/page.tsx

@@ -52,7 +52,7 @@ function BindForm() {
         <CardTitle className="text-center">绑定本地账号</CardTitle>
       </CardHeader>
       <CardContent className="space-y-4">
-        <p className="text-sm text-gray-500">
+        <p className="text-sm text-muted-foreground">
           您的 Keycloak 账号（{keycloakEmail || keycloakId}）尚未绑定本地账户。
           请输入已有的本地账号密码完成绑定。
         </p>
@@ -76,7 +76,7 @@ function BindForm() {
               required
             />
           </div>
-          {error && <p className="text-sm text-red-500">{error}</p>}
+          {error && <p className="text-sm text-destructive">{error}</p>}
           <Button type="submit" className="w-full">
             绑定并登录
           </Button>
@@ -88,8 +88,8 @@ function BindForm() {
 
 export default function BindAccountPage() {
   return (
-    <div className="flex min-h-screen items-center justify-center bg-gray-50 p-4">
-      <Suspense fallback={<div>加载中...</div>}>
+    <div className="flex min-h-screen items-center justify-center bg-gradient-to-br from-background via-background to-muted/40 p-4">
+      <Suspense fallback={<div className="text-sm text-muted-foreground">加载中...</div>}>
         <BindForm />
       </Suspense>
     </div>