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/constants/index.ts

@@ -0,0 +1,11 @@
+export const TAB_ORDER = ['Dashboard', 'DarkWatch', 'SpamShield', 'VoicePrint', 'Settings'] as const;
+
+export const AUTH_STORAGE_KEY = '@shieldai_auth';
+export const BIOMETRIC_ENABLED_KEY = '@shieldai_biometric';
+export const ONBOARDING_COMPLETE_KEY = '@shieldai_onboarding';
+
+export const NOTIFICATION_TYPES = {
+  DARKWATCH_ALERT: 'darkwatch_alert',
+  SPAM_BLOCKED: 'spam_blocked',
+  VOICEPRINT_ANALYSIS: 'voiceprint_analysis',
+} as const;