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/components/channel-model-manager.tsx

@@ -3,7 +3,7 @@ import { App, Button, Checkbox, Input, Modal, Popconfirm, Select, Space } from "
 import type { ColumnsType } from "antd/es/table";
 import { Plus, RefreshCw, Search, Trash2 } from "lucide-react";
 
-import { PaginationBar } from "@/components/layout/workspace-page";
+import { PaginationBar } from "@/pages/admin/components/admin-ui";
 import { ModelIcon } from "@/components/model-picker";
 import { modelProtocolDefinition, modelProtocolLabel, type ModelProtocol } from "@/lib/model-protocols";
 import { fetchPluginProviderCatalog } from "@/services/api/plugin-catalog";