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/Export/Views/ShareButton.swift

@@ -16,6 +16,11 @@ struct ShareButton<Content: ShareableContent>: View {
     var body: some View {
         Button {
             showPreview = true
+            if let tripContent = content as? TripShareContent {
+                AnalyticsManager.shared.track(.tripShared(tripId: tripContent.trip.id.uuidString))
+            } else if content is ProgressShareContent {
+                AnalyticsManager.shared.track(.progressCardShared(sport: "unknown"))
+            }
         } label: {
             switch style {
             case .icon: