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/theme.ts

@@ -0,0 +1,84 @@
+export const COLORS = {
+  primary: '#4f8cff',
+  primaryDark: '#3a6fd8',
+  secondary: '#6c5ce7',
+  accent: '#00cec9',
+  success: '#00b894',
+  warning: '#fdcb6e',
+  danger: '#ff6b6b',
+  background: '#0a0e1a',
+  backgroundLight: '#111827',
+  card: '#1a2035',
+  cardLight: '#243049',
+  text: '#e8eaf0',
+  textSecondary: '#8b95a8',
+  textMuted: '#5a6577',
+  border: '#2a3550',
+  overlay: 'rgba(0, 0, 0, 0.6)',
+} as const;
+
+export const SPACING = {
+  xs: 4,
+  sm: 8,
+  md: 16,
+  lg: 24,
+  xl: 32,
+  xxl: 48,
+} as const;
+
+export const FONT_SIZES = {
+  xs: 12,
+  sm: 14,
+  md: 16,
+  lg: 18,
+  xl: 20,
+  xxl: 24,
+  xxxl: 32,
+} as const;
+
+export const BORDER_RADIUS = {
+  sm: 4,
+  md: 8,
+  lg: 12,
+  xl: 16,
+  round: 999,
+} as const;
+
+export const SHADOWS = {
+  sm: { shadowColor: '#000', shadowOffset: { width: 0, height: 1 }, shadowOpacity: 0.1, shadowRadius: 2, elevation: 2 },
+  md: { shadowColor: '#000', shadowOffset: { width: 0, height: 2 }, shadowOpacity: 0.15, shadowRadius: 4, elevation: 4 },
+  lg: { shadowColor: '#000', shadowOffset: { width: 0, height: 4 }, shadowOpacity: 0.2, shadowRadius: 8, elevation: 8 },
+} as const;
+
+export const API_URL = process.env.EXPO_PUBLIC_API_URL || 'https://api.shieldai.freno.me/api/v1';
+
+export const TIER_FEATURES = {
+  free: {
+    name: 'Free',
+    maxExposures: 5,
+    spamProtection: false,
+    voicePrint: false,
+    darkWatch: false,
+  },
+  basic: {
+    name: 'Basic',
+    maxExposures: 50,
+    spamProtection: true,
+    voicePrint: false,
+    darkWatch: true,
+  },
+  premium: {
+    name: 'Premium',
+    maxExposures: 200,
+    spamProtection: true,
+    voicePrint: true,
+    darkWatch: true,
+  },
+  enterprise: {
+    name: 'Enterprise',
+    maxExposures: -1,
+    spamProtection: true,
+    voicePrint: true,
+    darkWatch: true,
+  },
+} as const;