Refactor observability and analytics documentation

- Updated the crash reporting section to clarify the integration of Bugly and sensors analytics.
- Revised the logging rules to ensure sensitive data is scrubbed before logging.
- Enhanced the session management guidelines to ensure user context is correctly set during login and logout processes.
- Consolidated the analytics event tracking strategy, emphasizing backend-driven event logging.
- Removed references to third-party SDKs for crash reporting and analytics, focusing on internal logging mechanisms.

flutter-app/04-routing.md

@@ -37,7 +37,7 @@ final goRouterProvider = Provider<GoRouter>((ref) {
   final router = GoRouter(
     navigatorKey: rootNavigatorKey, // 全局 dialog / 顶层跳转需要它
     initialLocation: '/home',
-    observers: [NavigationObserver(ref.read(crashReporterProvider))], // 崩溃前的页面路径，见 13
+    observers: const [], // 路由观测由 app 层按需注入
     redirect: (context, state) {
       // read 不是 watch：这里只要当前值，订阅由下面的 listen 负责
       final auth = ref.read(authStateProvider);