feat: scaffold ShieldAI React Native mobile app MVP (FRE-4572)

Build complete Expo/React Native mobile app with:
- Auth flow: email/password login, registration, biometric auth
- Dashboard: exposure summary, spam stats, voice protection status
- DarkWatch: watch list management, exposure feed, alert toggles
- SpamShield: call/text history, whitelist/blacklist management
- VoicePrint: family member enrollment, voice analysis
- Settings: tier management, notification preferences, security
- Push notification integration via FCM/APNs
- Offline-first state management with Zustand + AsyncStorage
- Integration with @shieldai/mobile-api-client for API services
- React Navigation with auth-aware routing (stack + bottom tabs)
- Dark theme with consistent design system (colors, spacing, typography)
- Network status monitoring and offline request queuing

Co-Authored-By: Paperclip <noreply@paperclip.ing>

packages/mobile/App.tsx

@@ -0,0 +1,29 @@
+import React, { useEffect } from 'react';
+import { StatusBar } from 'expo-status-bar';
+import { NavigationContainer } from '@react-navigation/native';
+import { GestureHandlerRootView } from 'react-native-gesture-handler';
+import { useAuthStore } from '@/store/authStore';
+import { AuthNavigator } from '@/navigation/AuthNavigator';
+import { MainTabNavigator } from '@/navigation/MainTabNavigator';
+import { usePushNotifications } from '@/hooks';
+import '@/services/api';
+
+export default function App() {
+  const { isAuthenticated } = useAuthStore();
+  const { registerForPushNotifications } = usePushNotifications();
+
+  useEffect(() => {
+    if (isAuthenticated) {
+      registerForPushNotifications();
+    }
+  }, [isAuthenticated, registerForPushNotifications]);
+
+  return (
+    <GestureHandlerRootView style={{ flex: 1 }}>
+      <NavigationContainer>
+        <StatusBar style="light" />
+        {isAuthenticated ? <MainTabNavigator /> : <AuthNavigator />}
+      </NavigationContainer>
+    </GestureHandlerRootView>
+  );
+}