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/Contractor/ContractorFormSheet.swift

@@ -292,7 +292,7 @@ struct ContractorFormSheet: View {
             .onAppear {
                 // Track screen view for new contractors
                 if contractor == nil {
-                    PostHogAnalytics.shared.screen(AnalyticsEvents.newContractorScreenShown)
+                    AnalyticsManager.shared.trackScreen(.newContractor)
                 }
                 residenceViewModel.loadMyResidences()
                 loadContractorData()
@@ -504,7 +504,7 @@ struct ContractorFormSheet: View {
             viewModel.createContractor(request: request) { success in
                 if success {
                     // Track contractor creation
-                    PostHogAnalytics.shared.capture(AnalyticsEvents.contractorCreated)
+                    AnalyticsManager.shared.track(.contractorCreated)
                     onSave()
                     dismiss()
                 }