Replace PostHog integration with AnalyticsManager architecture

Remove old PostHogAnalytics singleton and replace with guide-based
two-file architecture: AnalyticsManager (singleton wrapper with super
properties, session replay, opt-out, subscription funnel) and
AnalyticsEvent (type-safe enum with associated values).

Key changes:
- New API key, self-hosted analytics endpoint
- All 19 events ported to type-safe AnalyticsEvent enum
- Screen tracking via AnalyticsManager.Screen enum + SwiftUI modifier
- Remove all identify() calls — fully anonymous analytics
- Add lifecycle hooks: flush on background, update super properties on foreground
- Add privacy opt-out toggle in Settings
- Subscription funnel methods ready for IAP integration

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/iosApp/Task/TaskFormView.swift

@@ -311,7 +311,7 @@ struct TaskFormView: View {
             .onAppear {
                 // Track screen view for new tasks
                 if !isEditMode {
-                    PostHogAnalytics.shared.screen(AnalyticsEvents.newTaskScreenShown)
+                    AnalyticsManager.shared.trackScreen(.newTask)
                 }
                 // Set defaults when lookups are available
                 if dataManager.lookupsInitialized {
@@ -521,7 +521,7 @@ struct TaskFormView: View {
             viewModel.createTask(request: request) { success in
                 if success {
                     // Track task creation
-                    PostHogAnalytics.shared.capture(AnalyticsEvents.taskCreated, properties: ["residence_id": actualResidenceId])
+                    AnalyticsManager.shared.track(.taskCreated(residenceId: actualResidenceId))
                     // View will dismiss automatically via onChange
                 }
             }