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/_layout.tsx

@@ -0,0 +1,173 @@
+import React, { useEffect, useRef, useState } from 'react';
+import { AppState, AppStateStatus, Platform, View, ActivityIndicator, StyleSheet } from 'react-native';
+import { Stack, useRouter } from 'expo-router';
+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';
+
+import { paperTheme } from '../src/theme';
+import { AppBackButton } from '../src/components/common';
+import AppPromptBar from '../src/components/common/AppPromptBar';
+import AppDialogHost from '../src/components/common/AppDialogHost';
+import { installAlertOverride } from '../src/services/alertOverride';
+import { useAuthStore } from '../src/stores';
+import { colors } from '../src/theme';
+
+Notifications.setNotificationHandler({
+  handleNotification: async () => ({
+    shouldShowAlert: true,
+    shouldPlaySound: true,
+    shouldSetBadge: true,
+    shouldShowBanner: true,
+    shouldShowList: true,
+  }),
+});
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      retry: 2,
+      staleTime: 5 * 60 * 1000,
+    },
+  },
+});
+
+installAlertOverride();
+
+if (Platform.OS === 'web' && typeof document !== 'undefined') {
+  const style = document.createElement('style');
+  style.textContent = `
+    input:focus, textarea:focus, select:focus {
+      outline: none !important;
+      outline-width: 0 !important;
+      box-shadow: none !important;
+    }
+    input:focus-visible, textarea:focus-visible {
+      outline: none !important;
+    }
+    *:focus { outline: none !important; }
+    *:focus-visible { outline: none !important; }
+  `;
+  document.head.appendChild(style);
+}
+
+function SessionGate({ children }: { children: React.ReactNode }) {
+  const [ready, setReady] = useState(false);
+  const fetchCurrentUser = useAuthStore((s) => s.fetchCurrentUser);
+
+  useEffect(() => {
+    fetchCurrentUser().finally(() => setReady(true));
+  }, [fetchCurrentUser]);
+
+  if (!ready) {
+    return (
+      <View style={gateStyles.loading}>
+        <ActivityIndicator size="large" color={colors.primary.main} />
+      </View>
+    );
+  }
+  return <>{children}</>;
+}
+
+function NotificationBootstrap() {
+  const appState = useRef<AppStateStatus>(AppState.currentState);
+  const notificationResponseListener = useRef<Notifications.EventSubscription | null>(null);
+
+  useEffect(() => {
+    const initNotifications = async () => {
+      const { systemNotificationService } = await import('../src/services/systemNotificationService');
+      await systemNotificationService.initialize();
+      const { initBackgroundService } = await import('../src/services/backgroundService');
+      await initBackgroundService();
+
+      const subscription = AppState.addEventListener('change', (nextAppState) => {
+        if (appState.current.match(/inactive|background/) && nextAppState === 'active') {
+          systemNotificationService.clearBadge();
+        }
+        appState.current = nextAppState;
+      });
+
+      notificationResponseListener.current = Notifications.addNotificationResponseReceivedListener(
+        (response) => {
+          void response.notification.request.content.data;
+        }
+      );
+
+      const notificationReceivedSubscription = Notifications.addNotificationReceivedListener(
+        (notification) => {
+          void notification;
+        }
+      );
+
+      return () => {
+        subscription.remove();
+        notificationResponseListener.current?.remove();
+        notificationReceivedSubscription.remove();
+      };
+    };
+
+    initNotifications();
+  }, []);
+
+  return null;
+}
+
+export default function RootLayout() {
+  const router = useRouter();
+
+  return (
+    <GestureHandlerRootView style={{ flex: 1 }}>
+      <SafeAreaProvider>
+        <PaperProvider theme={paperTheme}>
+          <QueryClientProvider client={queryClient}>
+            <StatusBar style="light" />
+            <SessionGate>
+              <NotificationBootstrap />
+              <Stack screenOptions={{ headerShown: false }}>
+                <Stack.Screen name="index" options={{ headerShown: false }} />
+                <Stack.Screen name="(auth)" options={{ headerShown: false }} />
+                <Stack.Screen name="(app)" options={{ headerShown: false }} />
+                <Stack.Screen
+                  name="post/[postId]"
+                  options={{
+                    headerShown: true,
+                    title: '',
+                    headerStyle: { backgroundColor: colors.background.paper },
+                    headerTintColor: colors.text.primary,
+                    headerBackVisible: false,
+                    headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+                  }}
+                />
+                <Stack.Screen
+                  name="user/[userId]"
+                  options={{
+                    headerShown: true,
+                    title: '用户主页',
+                    headerStyle: { backgroundColor: colors.background.paper },
+                    headerTintColor: colors.text.primary,
+                    headerBackVisible: false,
+                    headerLeft: () => <AppBackButton onPress={() => router.back()} />,
+                  }}
+                />
+              </Stack>
+            </SessionGate>
+            <AppPromptBar />
+            <AppDialogHost />
+          </QueryClientProvider>
+        </PaperProvider>
+      </SafeAreaProvider>
+    </GestureHandlerRootView>
+  );
+}
+
+const gateStyles = StyleSheet.create({
+  loading: {
+    flex: 1,
+    justifyContent: 'center',
+    alignItems: 'center',
+    backgroundColor: colors.background.default,
+  },
+});