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/pages/Relay.tsx

@@ -0,0 +1,109 @@
+// ============================================================
+// 中转任务
+// ============================================================
+
+import { useQuery } from '@tanstack/react-query'
+import { Tag, Select, Typography } from 'antd'
+import type { ProColumns } from '@ant-design/pro-components'
+import { ProTable } from '@ant-design/pro-components'
+import { relayService } from '@/services/relay'
+import { useState } from 'react'
+import type { RelayTask } from '@/types'
+
+const { Title } = Typography
+
+const statusLabels: Record<string, string> = {
+  queued: '排队中',
+  running: '运行中',
+  completed: '已完成',
+  failed: '失败',
+  cancelled: '已取消',
+}
+
+const statusColors: Record<string, string> = {
+  queued: 'default',
+  running: 'processing',
+  completed: 'green',
+  failed: 'red',
+  cancelled: 'default',
+}
+
+export default function Relay() {
+  const [statusFilter, setStatusFilter] = useState<string | undefined>(undefined)
+  const [page, setPage] = useState(1)
+
+  const { data, isLoading } = useQuery({
+    queryKey: ['relay-tasks', page, statusFilter],
+    queryFn: () => relayService.list({ page, page_size: 20, status: statusFilter }),
+  })
+
+  const columns: ProColumns<RelayTask>[] = [
+    { title: 'ID', dataIndex: 'id', width: 120, render: (_, r) => <code>{r.id.substring(0, 8)}...</code> },
+    {
+      title: '状态',
+      dataIndex: 'status',
+      width: 100,
+      render: (_, r) => <Tag color={statusColors[r.status] || 'default'}>{statusLabels[r.status] || r.status}</Tag>,
+    },
+    { title: '模型', dataIndex: 'model_id', width: 160 },
+    { title: '优先级', dataIndex: 'priority', width: 70 },
+    { title: '尝试次数', dataIndex: 'attempt_count', width: 80 },
+    {
+      title: 'Token',
+      width: 140,
+      render: (_, r) => `${r.input_tokens.toLocaleString()} / ${r.output_tokens.toLocaleString()}`,
+    },
+    { title: '错误信息', dataIndex: 'error_message', width: 200, ellipsis: true },
+    {
+      title: '排队时间',
+      dataIndex: 'queued_at',
+      width: 180,
+      render: (_, r) => new Date(r.queued_at).toLocaleString('zh-CN'),
+    },
+    {
+      title: '完成时间',
+      dataIndex: 'completed_at',
+      width: 180,
+      render: (_, r) => r.completed_at ? new Date(r.completed_at).toLocaleString('zh-CN') : '-',
+    },
+  ]
+
+  return (
+    <div>
+      <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center', marginBottom: 24 }}>
+        <Title level={4} style={{ margin: 0 }}>中转任务</Title>
+        <Select
+          value={statusFilter}
+          onChange={(v) => { setStatusFilter(v === 'all' ? undefined : v); setPage(1) }}
+          placeholder="状态筛选"
+          style={{ width: 140 }}
+          allowClear
+          options={[
+            { value: 'all', label: '全部' },
+            { value: 'queued', label: '排队中' },
+            { value: 'running', label: '运行中' },
+            { value: 'completed', label: '已完成' },
+            { value: 'failed', label: '失败' },
+            { value: 'cancelled', label: '已取消' },
+          ]}
+        />
+      </div>
+
+      <ProTable<RelayTask>
+        columns={columns}
+        dataSource={data?.items ?? []}
+        loading={isLoading}
+        rowKey="id"
+        search={false}
+        toolBarRender={false}
+        pagination={{
+          total: data?.total ?? 0,
+          pageSize: 20,
+          current: page,
+          onChange: setPage,
+          showSizeChanger: false,
+        }}
+      />
+    </div>
+  )
+}