refactor(navigation): replace direct navigation with navigation service

Replace direct `navigation.navigate()` and `navigation.getParent()?.navigate()` calls with centralized `navigationService.navigate()` across multiple screens. Convert screen component functions from JSX elements to array-returning functions in RootNavigator to fix React key warnings and improve render consistency.

- HomeScreen: use navigationService for post and user navigation
- PrivateChatInfoScreen: use navigationService for profile navigation
- ChatScreen: use navigationService for avatar press and user profile navigation
- RootNavigator: convert PublicScreens and AuthenticatedScreens to getPublicScreens() and getAuthenticatedScreens() functions returning arrays with proper keys

src/screens/home/HomeScreen.tsx

@@ -35,6 +35,7 @@ import { HomeStackParamList, RootStackParamList } from '../../navigation/types';
 import { useResponsive, useResponsiveSpacing } from '../../hooks/useResponsive';
 import { SearchScreen } from './SearchScreen';
 import { CreatePostScreen } from '../create/CreatePostScreen';
+import { navigationService } from '../../infrastructure/navigation/navigationService';
 
 type NavigationProp = NativeStackNavigationProp<HomeStackParamList, 'Home'> & NativeStackNavigationProp<RootStackParamList>;
 
@@ -343,12 +344,12 @@ export const HomeScreen: React.FC = () => {
 
   // 跳转到帖子详情
   const handlePostPress = (postId: string, scrollToComments: boolean = false) => {
-    navigation.getParent()?.navigate('PostDetail', { postId, scrollToComments });
+    navigationService.navigate('PostDetail', { postId, scrollToComments });
   };
 
   // 跳转到用户主页
   const handleUserPress = (userId: string) => {
-    navigation.getParent()?.navigate('UserProfile', { userId });
+    navigationService.navigate('UserProfile', { userId });
   };
 
   // 点赞帖子