feat(navigation): add profile stack navigator and fix API endpoints

- Add ProfileStackNavigatorComponent with full navigation stack (Profile, Settings, EditProfile, AccountSecurity, MyPosts, Bookmarks, NotificationSettings, BlockedUsers)
- Add null checks for response data in authService login, register, and refreshToken methods
- Fix postService API routes to use correct endpoints (/posts instead of /posts/cursor)
- Remove completed cursor pagination design document

src/services/authService.ts

@@ -150,6 +150,9 @@ class AuthService {
   async login(data: LoginRequest): Promise<AuthResponse> {
     const response = await api.post<AuthResponse>('/auth/login', data);
 
+    if (!response.data) {
+      throw new Error('登录响应数据为空');
+    }
     if (response.data.token) {
       await api.setToken(response.data.token);
     }
@@ -165,6 +168,9 @@ class AuthService {
   async register(data: RegisterRequest): Promise<AuthResponse> {
     const response = await api.post<AuthResponse>('/auth/register', data);
 
+    if (!response.data) {
+      throw new Error('注册响应数据为空');
+    }
     if (response.data.token) {
       await api.setToken(response.data.token);
     }
@@ -233,6 +239,9 @@ class AuthService {
     try {
       const response = await api.post<RefreshTokenResponse>('/auth/refresh');
       
+      if (!response.data) {
+        return null;
+      }
       if (response.data.token) {
         await api.setToken(response.data.token);
       }