Add Android onboarding flow matching iOS implementation

Implement complete onboarding experience for Android with the following screens:
- Welcome screen with "Start Fresh" and "Join Existing Home" options
- Value props carousel showcasing app features (Tasks, Documents, Contractors, Family)
- Residence naming screen for new property setup
- Account creation with email registration (no Apple Sign In on Android)
- Email verification with 6-digit code
- Join residence screen for share code entry
- First task selection with 6 category templates
- Subscription upsell with monthly/yearly plans

Key implementation details:
- OnboardingViewModel manages all state and API integration
- AnimatedContent provides smooth screen transitions
- HorizontalPager for feature carousel
- Onboarding completion persisted in DataManager
- New users start at onboarding, returning users go to login

Files added:
- OnboardingViewModel.kt
- OnboardingScreen.kt (coordinator)
- OnboardingWelcomeContent.kt
- OnboardingValuePropsContent.kt
- OnboardingNameResidenceContent.kt
- OnboardingCreateAccountContent.kt
- OnboardingVerifyEmailContent.kt
- OnboardingJoinResidenceContent.kt
- OnboardingFirstTaskContent.kt
- OnboardingSubscriptionContent.kt

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

composeApp/src/commonMain/kotlin/com/example/casera/navigation/Routes.kt

@@ -118,3 +118,7 @@ object ResetPasswordRoute
 
 @Serializable
 object NotificationPreferencesRoute
+
+// Onboarding Routes
+@Serializable
+object OnboardingRoute