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/login/login-form.tsx

@@ -66,7 +66,7 @@ export function LoginForm({
             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">
           本地账号登录
         </Button>
@@ -76,14 +76,15 @@ export function LoginForm({
         <>
           <div className="relative">
             <div className="absolute inset-0 flex items-center">
-              <span className="w-full border-t" />
+              <span className="w-full border-t border-border" />
             </div>
             <div className="relative flex justify-center text-xs uppercase">
-              <span className="bg-white px-2 text-gray-500">或者</span>
+              <span className="bg-popover px-2 text-muted-foreground">或者</span>
             </div>
           </div>
 
           <Button
+            type="button"
             variant="outline"
             className="w-full"
             onClick={() => signIn("keycloak", { callbackUrl })}