feat(admin): Admin V2 — Ant Design Pro 纯 SPA 重写

Next.js SSR/hydration 与 SWR fetch-on-mount 存在根本冲突：
hydration 卸载组件时 abort 的请求仍占用后端 DB 连接，
retry 循环耗尽 PostgreSQL 连接池导致后端完全卡死。

admin-v2 使用 Vite + React + antd 纯 SPA 彻底消除此问题：
- 12 页面全部完成（Login, Dashboard, Accounts, Providers, Models,
  API Keys, Usage, Relay, Config, Prompts, Logs, Agent Templates）
- ProTable + ProForm + ProLayout 统一 UI 模式
- TanStack Query + Axios + Zustand 数据层
- JWT 自动刷新 + 401 重试机制
- 全部 18 网络请求 200 OK，零 ERR_ABORTED

同时更新 troubleshooting 第 13 节和 SaaS 平台文档。

admin-v2/src/router/index.tsx

@@ -0,0 +1,35 @@
+// ============================================================
+// 路由定义
+// ============================================================
+
+import { createBrowserRouter } from 'react-router-dom'
+import { AuthGuard } from './AuthGuard'
+import AdminLayout from '@/layouts/AdminLayout'
+
+export const router = createBrowserRouter([
+  {
+    path: '/login',
+    lazy: () => import('@/pages/Login').then((m) => ({ Component: m.default })),
+  },
+  {
+    path: '/',
+    element: (
+      <AuthGuard>
+        <AdminLayout />
+      </AuthGuard>
+    ),
+    children: [
+      { index: true, lazy: () => import('@/pages/Dashboard').then((m) => ({ Component: m.default })) },
+      { path: 'accounts', lazy: () => import('@/pages/Accounts').then((m) => ({ Component: m.default })) },
+      { path: 'providers', lazy: () => import('@/pages/Providers').then((m) => ({ Component: m.default })) },
+      { path: 'models', lazy: () => import('@/pages/Models').then((m) => ({ Component: m.default })) },
+      { path: 'agent-templates', lazy: () => import('@/pages/AgentTemplates').then((m) => ({ Component: m.default })) },
+      { path: 'api-keys', lazy: () => import('@/pages/ApiKeys').then((m) => ({ Component: m.default })) },
+      { path: 'usage', lazy: () => import('@/pages/Usage').then((m) => ({ Component: m.default })) },
+      { path: 'relay', lazy: () => import('@/pages/Relay').then((m) => ({ Component: m.default })) },
+      { path: 'config', lazy: () => import('@/pages/Config').then((m) => ({ Component: m.default })) },
+      { path: 'prompts', lazy: () => import('@/pages/Prompts').then((m) => ({ Component: m.default })) },
+      { path: 'logs', lazy: () => import('@/pages/Logs').then((m) => ({ Component: m.default })) },
+    ],
+  },
+])