feat: 首页添加性能监控

src/index.js

@@ -3,6 +3,10 @@ import React from 'react';
 import ReactDOM from 'react-dom/client';
 import { BrowserRouter as Router } from 'react-router-dom';
 
+// ⚡ 性能监控：在应用启动时尽早标记
+import { performanceMonitor } from './utils/performanceMonitor';
+performanceMonitor.mark('app-start');
+
 // 导入 Brainwave 样式（空文件，保留以避免错误）
 import './styles/brainwave.css';