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/src/hooks/usePushNotifications.ts

@@ -0,0 +1,65 @@
+import { useEffect, useCallback } from 'react';
+import * as Notifications from 'expo-notifications';
+import { Platform } from 'react-native';
+import { deviceService, notificationService } from '@shieldai/mobile-api-client';
+import { useSettingsStore } from '@/store/settingsStore';
+
+Notifications.setNotificationHandler({
+  handleNotification: async () => ({
+    shouldShowAlert: true,
+    shouldPlaySound: true,
+    shouldSetBadge: false,
+  }),
+});
+
+export function usePushNotifications() {
+  const { preferences } = useSettingsStore();
+
+  const registerForPushNotifications = useCallback(async () => {
+    try {
+      const { status: existingStatus } = await Notifications.getPermissionsAsync();
+      let finalStatus = existingStatus;
+
+      if (existingStatus !== 'granted') {
+        const { status } = await Notifications.requestPermissionsAsync();
+        finalStatus = status;
+      }
+
+      if (finalStatus !== 'granted') {
+        return null;
+      }
+
+      const token = (await Notifications.getExpoPushTokenAsync({
+        projectId: 'shieldai-project-id',
+      })).data;
+
+      await deviceService.registerDevice({
+        platform: Platform.OS === 'ios' ? 'ios' : 'android',
+        pushToken: token,
+        modelName: Platform.OS === 'ios' ? 'iPhone' : 'Android',
+        osVersion: Platform.Version.toString(),
+        appVersion: '1.0.0',
+      });
+
+      return token;
+    } catch (error) {
+      console.error('Failed to register for push notifications:', error);
+      return null;
+    }
+  }, []);
+
+  useEffect(() => {
+    const subscription = Notifications.addNotificationReceivedListener((notification) => {
+      const type = notification.request.content.data?.type;
+      const prefs = useSettingsStore.getState().preferences;
+
+      if (type === 'darkwatch_alert' && !prefs.darkwatchAlert) return;
+      if (type === 'spam_blocked' && !prefs.spamBlocked) return;
+      if (type === 'voiceprint_analysis' && !prefs.voiceprintAnalysis) return;
+    });
+
+    return () => subscription.remove();
+  }, []);
+
+  return { registerForPushNotifications };
+}