feat(analytics): 增强 Google Analytics 隐私合规与追踪功能

- 修复 allow_google_signals 配置为 false，禁用跨设备追踪
- 升级 Cookie 同意组件，支持三级偏好控制（必要/分析/营销）
- 新增滚动深度追踪组件，追踪 25%/50%/75%/100% 里程碑
- 更新隐私政策，新增 Cookie 和网站分析工具章节
- 新增细化同意管理函数，支持 PIPL 合规

src/lib/analytics.ts

@@ -149,6 +149,13 @@ export const trackProductView = (productId: string, productName: string) => {
   }
 };
 
+export interface CookiePreferences {
+  necessary: boolean;
+  analytics: boolean;
+  marketing: boolean;
+  timestamp: number;
+}
+
 export const updateConsent = (granted: boolean) => {
   if (typeof window !== 'undefined' && window.gtag) {
     window.gtag('consent', 'update', {
@@ -157,3 +164,44 @@ export const updateConsent = (granted: boolean) => {
     });
   }
 };
+
+export const updateConsentDetailed = (preferences: CookiePreferences) => {
+  if (typeof window !== 'undefined' && window.gtag) {
+    window.gtag('consent', 'update', {
+      analytics_storage: preferences.analytics ? 'granted' : 'denied',
+      ad_storage: preferences.marketing ? 'granted' : 'denied',
+      functionality_storage: 'granted',
+      personalization_storage: preferences.marketing ? 'granted' : 'denied',
+      security_storage: 'granted',
+    });
+  }
+};
+
+export const getStoredPreferences = (): CookiePreferences | null => {
+  if (typeof window === 'undefined') {
+    return null;
+  }
+
+  try {
+    const stored = localStorage.getItem('cookie_preferences');
+    if (stored) {
+      return JSON.parse(stored) as CookiePreferences;
+    }
+  } catch {
+    return null;
+  }
+  return null;
+};
+
+export const storePreferences = (preferences: CookiePreferences) => {
+  if (typeof window !== 'undefined') {
+    localStorage.setItem('cookie_preferences', JSON.stringify(preferences));
+  }
+};
+
+export const getDefaultPreferences = (): CookiePreferences => ({
+  necessary: true,
+  analytics: false,
+  marketing: false,
+  timestamp: Date.now(),
+});