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/.gitignore

@@ -0,0 +1,20 @@
+node_modules/
+.expo/
+.expo-shared/
+dist/
+ios/
+android/
+*.jks
+*.p8
+*.p12
+*.mobileprovision
+*.orig.*
+*.pub
+.jscache
+*.log
+*.pid
+*.tgz
+*.npm
+*.lock
+.DS_Store
+.env