refactor(App, navigation): migrate to Expo Router and clean up navigation structure

- Updated App entry point to utilize Expo Router, simplifying the navigation setup.
- Removed legacy navigation components and services to streamline the codebase.
- Adjusted package.json to reflect the new entry point and updated dependencies for compatibility.
- Enhanced overall application structure by consolidating navigation logic and improving maintainability.

App.tsx

@@ -1,137 +1,7 @@
 /**
- * 萝卜BBS - 主应用入口
- * 配置导航、主题、状态管理等
+ * 应用入口已由 Expo Router 接管（package.json main: expo-router/entry）。
+ * 全局 Provider 与根布局见 app/_layout.tsx。
  */
-
-import React, { useEffect, useRef } from 'react';
-import { AppState, AppStateStatus, Platform, StyleSheet } from 'react-native';
-import { StatusBar } from 'expo-status-bar';
-import { GestureHandlerRootView } from 'react-native-gesture-handler';
-import { SafeAreaProvider } from 'react-native-safe-area-context';
-import { PaperProvider } from 'react-native-paper';
-import { QueryClient, QueryClientProvider } from '@tanstack/react-query';
-import * as Notifications from 'expo-notifications';
-
-// 配置通知处理器 - 必须在应用启动时设置
-Notifications.setNotificationHandler({
-  handleNotification: async () => ({
-    shouldShowAlert: true,       // 即使在后台也要显示通知
-    shouldPlaySound: true,       // 播放声音
-    shouldSetBadge: true,        // 设置角标
-    shouldShowBanner: true,      // 显示横幅
-    shouldShowList: true,        // 显示通知列表
-  }),
-});
-
-import MainNavigator from './src/navigation/MainNavigator';
-import { paperTheme } from './src/theme';
-import AppPromptBar from './src/components/common/AppPromptBar';
-import AppDialogHost from './src/components/common/AppDialogHost';
-import { installAlertOverride } from './src/services/alertOverride';
-// 数据库初始化移到 authStore 中，根据用户ID创建用户专属数据库
-
-// 创建 QueryClient 实例
-const queryClient = new QueryClient({
-  defaultOptions: {
-    queries: {
-      retry: 2,
-      staleTime: 5 * 60 * 1000, // 5分钟
-    },
-  },
-});
-
-installAlertOverride();
-
-// 注入全局CSS来移除React Native Web在浏览器中的默认focus outline
-if (Platform.OS === 'web') {
-  const style = document.createElement('style');
-  style.textContent = `
-    /* 移除TextInput focus时的浏览器默认outline */
-    input:focus, textarea:focus, select:focus {
-      outline: none !important;
-      outline-width: 0 !important;
-      box-shadow: none !important;
-    }
-    
-    /* 移除focus-visible时的默认outline */
-    input:focus-visible, textarea:focus-visible {
-      outline: none !important;
-    }
-    
-    /* 移除所有:focus相关的默认样式 */
-    *:focus {
-      outline: none !important;
-    }
-    
-    *:focus-visible {
-      outline: none !important;
-    }
-  `;
-  document.head.appendChild(style);
-}
-
 export default function App() {
-  const appState = useRef<AppStateStatus>(AppState.currentState);
-  const notificationResponseListener = useRef<Notifications.EventSubscription | null>(null);
-
-  // 系统通知功能初始化
-  useEffect(() => {
-    const initNotifications = async () => {
-      const { systemNotificationService } = await import('./src/services/systemNotificationService');
-      await systemNotificationService.initialize();
-      
-      // 初始化后台保活服务
-      const { initBackgroundService } = await import('./src/services/backgroundService');
-      await initBackgroundService();
-      
-      // 监听 App 状态变化
-      const subscription = AppState.addEventListener('change', (nextAppState) => {
-        if (
-          appState.current.match(/inactive|background/) &&
-          nextAppState === 'active'
-        ) {
-          systemNotificationService.clearBadge();
-        }
-        appState.current = nextAppState;
-      });
-
-      // 监听通知点击响应
-      notificationResponseListener.current = Notifications.addNotificationResponseReceivedListener(
-        (response) => {
-          const data = response.notification.request.content.data;
-          void data;
-        }
-      );
-      
-      // 监听通知到达（用于前台显示时额外处理）
-      const notificationReceivedSubscription = Notifications.addNotificationReceivedListener(
-        (notification) => {
-          void notification;
-        }
-      );
-
-      return () => {
-        subscription.remove();
-        notificationResponseListener.current?.remove();
-        notificationReceivedSubscription.remove();
-      };
-    };
-
-    initNotifications();
-  }, []);
-
-  return (
-    <GestureHandlerRootView style={{ flex: 1 }}>
-      <SafeAreaProvider>
-        <PaperProvider theme={paperTheme}>
-          <QueryClientProvider client={queryClient}>
-            <StatusBar style="light" />
-            <MainNavigator />
-            <AppPromptBar />
-            <AppDialogHost />
-          </QueryClientProvider>
-        </PaperProvider>
-      </SafeAreaProvider>
-    </GestureHandlerRootView>
-  );
+  return null;
 }