feat(android): implement auth screens, onboarding flow, and account setup
- Add AuthRepository with EncryptedSharedPreferences and OkHttp API calls
- Add AuthViewModel with login/signup/reset/Google Sign-In flows
- Create auth screens: AuthScreen, LoginScreen, SignupScreen,
ForgotPasswordScreen, ResetPasswordScreen, BiometricAuthScreen
- Create onboarding screens with HorizontalPager: PlanSelection,
WatchlistSetup, FamilyInvite, Complete (with checkmark animation)
- Wire auth state to navigation: unauthenticated→auth, new→onboarding,
authenticated→dashboard
- Add PasswordStrength utility with tests
- Add dependencies: security-crypto, biometric, play-services-auth,
okhttp, gson, lottie-compose, material-icons-core
- Add unit tests: 23 tests passing for AuthViewModel and PasswordStrength