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/Task/TaskFormView.swift

@@ -312,6 +312,10 @@ struct TaskFormView: View {
                 }
             }
             .onAppear {
+                // Track screen view for new tasks
+                if !isEditMode {
+                    PostHogAnalytics.shared.screen(AnalyticsEvents.newTaskScreenShown)
+                }
                 // Set defaults when lookups are available
                 if dataManager.lookupsInitialized {
                     setDefaults()
@@ -520,6 +524,8 @@ struct TaskFormView: View {
 
             viewModel.createTask(request: request) { success in
                 if success {
+                    // Track task creation
+                    PostHogAnalytics.shared.capture(AnalyticsEvents.taskCreated, properties: ["residence_id": actualResidenceId])
                     // View will dismiss automatically via onChange
                 }
             }