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/package.json

@@ -10,7 +10,8 @@
   },
   "dependencies": {
     "react": "^18.3.1",
-    "react-dom": "^18.3.1"
+    "react-dom": "^18.3.1",
+    "react-router-dom": "^6.30.6"
   },
   "devDependencies": {
     "@types/react": "^18.3.3",