Add PostHog analytics integration for Android and iOS

Implement comprehensive analytics tracking across both platforms:

Android (Kotlin):
- Add PostHog SDK dependency and initialization in MainActivity
- Create expect/actual pattern for cross-platform analytics (commonMain/androidMain/iosMain/jvmMain/jsMain/wasmJsMain)
- Track screen views: registration, login, residences, tasks, contractors, documents, notifications, profile
- Track key events: user_registered, user_signed_in, residence_created, task_created, contractor_created, document_created
- Track paywall events: contractor_paywall_shown, documents_paywall_shown
- Track sharing events: residence_shared, contractor_shared
- Track theme_changed event

iOS (Swift):
- Add PostHog iOS SDK via SPM
- Create PostHogAnalytics wrapper and AnalyticsEvents constants
- Initialize SDK in iOSApp with session replay support
- Track same screen views and events as Android
- Track user identification after login/registration

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

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

iosApp/iosApp/ResidenceFormView.swift

@@ -230,6 +230,9 @@ struct ResidenceFormView: View {
                 }
             }
             .onAppear {
+                if !isEditMode {
+                    PostHogAnalytics.shared.screen(AnalyticsEvents.newResidenceScreenShown)
+                }
                 loadResidenceTypes()
                 initializeForm()
                 if isEditMode && isCurrentUserOwner {
@@ -368,6 +371,10 @@ struct ResidenceFormView: View {
             // Add mode
             viewModel.createResidence(request: request) { success in
                 if success {
+                    // Track residence created
+                    PostHogAnalytics.shared.capture(AnalyticsEvents.residenceCreated, properties: [
+                        "residence_type": selectedPropertyType?.name ?? "unknown"
+                    ])
                     onSuccess?()
                     isPresented = false
                 }