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/data/DataManager.kt

@@ -91,6 +91,11 @@ object DataManager {
     private val _themeId = MutableStateFlow("default")
     val themeId: StateFlow<String> = _themeId.asStateFlow()
 
+    // ==================== ONBOARDING ====================
+
+    private val _hasCompletedOnboarding = MutableStateFlow(false)
+    val hasCompletedOnboarding: StateFlow<Boolean> = _hasCompletedOnboarding.asStateFlow()
+
     // ==================== RESIDENCES ====================
 
     private val _residences = MutableStateFlow<List<Residence>>(emptyList())
@@ -256,6 +261,13 @@ object DataManager {
         themeManager?.saveThemeId(id)
     }
 
+    // ==================== ONBOARDING UPDATE METHODS ====================
+
+    fun setHasCompletedOnboarding(completed: Boolean) {
+        _hasCompletedOnboarding.value = completed
+        persistenceManager?.save(KEY_HAS_COMPLETED_ONBOARDING, completed.toString())
+    }
+
     // ==================== RESIDENCE UPDATE METHODS ====================
 
     fun setResidences(residences: List<Residence>) {
@@ -668,6 +680,11 @@ object DataManager {
             manager.load(KEY_CURRENT_USER)?.let { data ->
                 _currentUser.value = json.decodeFromString<User>(data)
             }
+
+            // Load onboarding completion flag
+            manager.load(KEY_HAS_COMPLETED_ONBOARDING)?.let { data ->
+                _hasCompletedOnboarding.value = data.toBooleanStrictOrNull() ?: false
+            }
         } catch (e: Exception) {
             println("DataManager: Error loading from disk: ${e.message}")
         }
@@ -677,4 +694,5 @@ object DataManager {
     // Only user data is persisted - all other data fetched fresh from API
 
     private const val KEY_CURRENT_USER = "dm_current_user"
+    private const val KEY_HAS_COMPLETED_ONBOARDING = "dm_has_completed_onboarding"
 }