feat: add PostHog analytics with full event tracking across app

Integrate self-hosted PostHog (SPM) with AnalyticsManager singleton wrapping
all SDK calls. Adds ~40 type-safe events covering trip planning, schedule,
progress, IAP, settings, polls, export, and share flows. Includes session
replay, autocapture, network telemetry, privacy opt-out toggle in Settings,
and super properties (app version, device, pro status, selected sports).

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

SportsTime/Features/Progress/Views/StadiumVisitSheet.swift

@@ -408,6 +408,7 @@ struct StadiumVisitSheet: View {
 
         do {
             try modelContext.save()
+            AnalyticsManager.shared.track(.stadiumVisitAdded(stadiumId: stadium.id, sport: selectedSport.rawValue))
             onSave?(visit)
             dismiss()
         } catch {