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/Paywall/Views/OnboardingPaywallView.swift

@@ -477,6 +477,9 @@ struct OnboardingPaywallView: View {
                 .padding(.bottom, Theme.Spacing.xl)
         }
         .background(Theme.backgroundGradient(colorScheme))
+        .onAppear {
+            AnalyticsManager.shared.track(.onboardingPaywallViewed)
+        }
     }
 
     // MARK: - Feature Page
@@ -556,7 +559,7 @@ struct OnboardingPaywallView: View {
     // MARK: - Pricing Page
 
     private var pricingPage: some View {
-        PaywallView()
+        PaywallView(source: "onboarding")
             .storeButton(.hidden, for: .cancellation)
     }
 
@@ -584,6 +587,7 @@ struct OnboardingPaywallView: View {
             // Continue free (always visible)
             Button {
                 markOnboardingSeen()
+                AnalyticsManager.shared.track(.onboardingPaywallDismissed)
                 isPresented = false
             } label: {
                 Text("Continue with Free")