feat(saas): Phase 2 Admin Web 管理后台 — 完整 CRUD + Dashboard 统计

后端:
- 添加 GET /api/v1/stats/dashboard 聚合统计端点
  (账号数/活跃服务商/今日请求/今日Token用量等7项指标)
- 需要 account:admin 权限

Admin 前端 (Next.js 14 + shadcn/ui + Tailwind + Recharts):
- 设计系统: Dark Mode OLED (#020617 背景, #22C55E CTA)
- 登录页: 双栏布局, 品牌区 + 表单
- Dashboard 布局: Sidebar 导航 + Header + 主内容区
- 仪表盘: 4 统计卡片 + AreaChart 请求趋势 + BarChart Token用量
- 8 个 CRUD 页面:
  - 账号管理 (搜索/角色/状态筛选, 编辑/启用禁用)
  - 服务商 (CRUD + API Key masked)
  - 模型管理 (Provider筛选, CRUD)
  - API 密钥 (创建/撤销, 一次性显示token)
  - 用量统计 (LineChart + BarChart)
  - 中转任务 (状态筛选, 展开详情)
  - 系统配置 (分类Tab, 编辑)
  - 操作日志 (Action筛选, 展开详情)
- 14 个 shadcn 风格 UI 组件 (手写实现)
- 类型化 API 客户端 (SaaSClient, 20+ 方法, 401 自动跳转)
- AuthGuard 路由保护 + useAuth() hook

验证: tsc --noEmit 零 error, pnpm build 13 页面成功, cargo test 21 通过

admin/src/components/ui/tabs.tsx

@@ -0,0 +1,57 @@
+'use client'
+
+import * as React from 'react'
+import * as TabsPrimitive from '@radix-ui/react-tabs'
+import { cn } from '@/lib/utils'
+
+const Tabs = TabsPrimitive.Root
+
+const TabsList = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.List>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.List>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.List
+    ref={ref}
+    className={cn(
+      'inline-flex h-9 items-center justify-center rounded-lg bg-muted p-1 text-muted-foreground',
+      className,
+    )}
+    {...props}
+  />
+))
+TabsList.displayName = TabsPrimitive.List.displayName
+
+const TabsTrigger = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.Trigger>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Trigger>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Trigger
+    ref={ref}
+    className={cn(
+      'inline-flex items-center justify-center whitespace-nowrap rounded-md px-3 py-1 text-sm font-medium ring-offset-background transition-all duration-200',
+      'focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2',
+      'disabled:pointer-events-none disabled:opacity-50',
+      'data-[state=active]:bg-card data-[state=active]:text-foreground data-[state=active]:shadow',
+      className,
+    )}
+    {...props}
+  />
+))
+TabsTrigger.displayName = TabsPrimitive.Trigger.displayName
+
+const TabsContent = React.forwardRef<
+  React.ElementRef<typeof TabsPrimitive.Content>,
+  React.ComponentPropsWithoutRef<typeof TabsPrimitive.Content>
+>(({ className, ...props }, ref) => (
+  <TabsPrimitive.Content
+    ref={ref}
+    className={cn(
+      'mt-2 ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2',
+      className,
+    )}
+    {...props}
+  />
+))
+TabsContent.displayName = TabsPrimitive.Content.displayName
+
+export { Tabs, TabsList, TabsTrigger, TabsContent }