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/store/settingsStore.ts

@@ -0,0 +1,40 @@
+import { create } from 'zustand';
+import { persist, createJSONStorage } from 'zustand/middleware';
+import AsyncStorage from '@react-native-async-storage/async-storage';
+import type { NotificationPreference } from '@/types';
+
+interface SettingsState {
+  preferences: NotificationPreference;
+  isBiometricEnabled: boolean;
+  updatePreferences: (prefs: Partial<NotificationPreference>) => void;
+  toggleBiometric: (enabled: boolean) => void;
+}
+
+const defaultPreferences: NotificationPreference = {
+  emailNotifications: true,
+  pushNotifications: true,
+  darkwatchAlert: true,
+  spamBlocked: true,
+  voiceprintAnalysis: true,
+};
+
+export const useSettingsStore = create<SettingsState>()(
+  persist(
+    (set) => ({
+      preferences: defaultPreferences,
+      isBiometricEnabled: false,
+
+      updatePreferences: (prefs) => {
+        set((state) => ({
+          preferences: { ...state.preferences, ...prefs },
+        }));
+      },
+
+      toggleBiometric: (enabled) => set({ isBiometricEnabled: enabled }),
+    }),
+    {
+      name: '@shieldai_settings',
+      storage: createJSONStorage(() => AsyncStorage),
+    }
+  )
+);