feat: PostHog 集成\

1. ✅ 安装依赖: posthog-js@^1.280.1
  2. ✅ 创建核心文件:
    - src/lib/posthog.js - PostHog SDK 封装（271 行）
    - src/lib/constants.js - 事件常量定义（AARRR 框架）
    - src/hooks/usePostHog.js - PostHog React Hook
    - src/hooks/usePageTracking.js - 页面追踪 Hook
    - src/components/PostHogProvider.js - Provider 组件
  3. ✅ 集成到应用:
    - 修改 src/App.js，在最外层添加 <PostHogProvider>
    - 自动追踪所有页面浏览
  4. ✅ 配置环境变量:
    - 在 .env 添加 PostHog 配置项
    - REACT_APP_POSTHOG_KEY 留空，需要用户填写
  5. ✅ 创建文档: POSTHOG_INTEGRATION.md 包含完整的使用说明

src/hooks/usePageTracking.js

@@ -0,0 +1,55 @@
+// src/hooks/usePageTracking.js
+import { useEffect, useRef } from 'react';
+import { useLocation } from 'react-router-dom';
+import posthog from 'posthog-js';
+
+/**
+ * Custom hook for automatic page view tracking with PostHog
+ *
+ * @param {Object} options - Configuration options
+ * @param {boolean} options.enabled - Whether tracking is enabled
+ * @param {Function} options.getProperties - Function to get custom properties for each page view
+ */
+export const usePageTracking = ({ enabled = true, getProperties } = {}) => {
+  const location = useLocation();
+  const previousPathRef = useRef('');
+
+  useEffect(() => {
+    if (!enabled) return;
+
+    // Get the current path
+    const currentPath = location.pathname + location.search;
+
+    // Skip if it's the same page (prevents duplicate tracking)
+    if (previousPathRef.current === currentPath) {
+      return;
+    }
+
+    // Update the previous path
+    previousPathRef.current = currentPath;
+
+    // Get custom properties if function provided
+    const customProperties = getProperties ? getProperties(location) : {};
+
+    // Track page view with PostHog
+    if (posthog && posthog.__loaded) {
+      posthog.capture('$pageview', {
+        $current_url: window.location.href,
+        path: location.pathname,
+        search: location.search,
+        hash: location.hash,
+        ...customProperties,
+      });
+
+      // Log in development
+      if (process.env.NODE_ENV === 'development') {
+        console.log('📊 PostHog $pageview:', {
+          path: location.pathname,
+          ...customProperties,
+        });
+      }
+    }
+  }, [location, enabled, getProperties]);
+};
+
+export default usePageTracking;