feat: 后台管理 Admin 仪表盘

新增完整的后台管理系统 (/admin):
- Dashboard: 系统概览、最近采集状态、预测统计
- Collection: 数据采集触发(bzzoiro/understat/injuries)
- Predictions: 预测历史查看、触发新预测
- Backtest: 回测配置与结果查看
- Monitoring: 系统健康、错误日志、死色队列
- Config: API Key 与数据源配置

技术栈: React Router + Tailwind 暗色主题 + TypeScript
文件: 11 个新文件, +21KB JS / +5KB CSS

frontend/src/admin/routes.tsx

@@ -0,0 +1,33 @@
+/**
+ * Admin 后台 - 路由配置
+ *
+ * 所有 Admin 页面的路由定义,使用嵌套路由。
+ * 挂载路径: /admin/*
+ */
+
+import { createBrowserRouter, Navigate } from 'react-router-dom'
+import AdminLayout from './AdminLayout'
+import Dashboard from './pages/Dashboard'
+import CollectionPage from './pages/Collection'
+import PredictionsPage from './pages/Predictions'
+import BacktestPage from './pages/Backtest'
+import MonitoringPage from './pages/Monitoring'
+import ConfigPage from './pages/Config'
+
+export const adminRoutes = [
+  {
+    path: '/admin',
+    element: <AdminLayout />,
+    children: [
+      { index: true, element: <Dashboard /> },
+      { path: 'collection', element: <CollectionPage /> },
+      { path: 'predictions', element: <PredictionsPage /> },
+      { path: 'backtest', element: <BacktestPage /> },
+      { path: 'monitoring', element: <MonitoringPage /> },
+      { path: 'config', element: <ConfigPage /> },
+      { path: '*', element: <Navigate to="/admin" replace /> },
+    ],
+  },
+]
+
+export { adminRoutes as default }