refactor(admin): 管理后台 UI - 独立设计系统并与用户端隔离

把后台 token、Ant 主题、壳层控件和抽屉弹窗从用户工作台拆开，去掉树状侧栏装饰线，色板仍用原来的中性黑白台阶。

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

web/src/pages/admin/settings/components/welcome-setting.tsx

@@ -1,6 +1,6 @@
 import { useEffect, useState } from "react";
 import { App, Button } from "antd";
-import { Switch } from "@/components/ui/base/switch";
+import { Switch } from "@/pages/admin/ui/controls";
 import { getAdminFeatureAvailability, updateAdminFeatureAvailability } from "@/services/api/auth";
 import { useUserStore } from "@/stores/use-user-store";