feat(store): add In-App Purchase system with Pro subscription

Implement freemium model with StoreKit 2:
- StoreManager singleton for purchase/restore/entitlements
- ProFeature enum defining gated features
- PaywallView and OnboardingPaywallView for upsell UI
- ProGate view modifier and ProBadge component

Feature gating:
- Trip saving: 1 free trip, then requires Pro
- PDF export: Pro only with badge indicator
- Progress tab: Shows ProLockedView for free users
- Settings: Subscription management section

Also fixes pre-existing test issues with StadiumVisit
and ItineraryOption model signature changes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Features/Trip/Views/TripDetailView.swift

@@ -14,6 +14,8 @@ struct TripDetailView: View {
     let trip: Trip
     let games: [String: RichGame]
 
+    @Query private var savedTrips: [SavedTrip]
+    @State private var showProPaywall = false
     @State private var selectedDay: ItineraryDay?
     @State private var showExportSheet = false
     @State private var showShareSheet = false
@@ -69,12 +71,21 @@ struct TripDetailView: View {
                 }
 
                 Button {
-                    Task {
-                        await exportPDF()
+                    if StoreManager.shared.isPro {
+                        Task {
+                            await exportPDF()
+                        }
+                    } else {
+                        showProPaywall = true
                     }
                 } label: {
-                    Image(systemName: "doc.fill")
-                        .foregroundStyle(Theme.warmOrange)
+                    HStack(spacing: 2) {
+                        Image(systemName: "doc.fill")
+                        if !StoreManager.shared.isPro {
+                            ProBadge()
+                        }
+                    }
+                    .foregroundStyle(Theme.warmOrange)
                 }
             }
         }
@@ -90,6 +101,9 @@ struct TripDetailView: View {
                 ShareSheet(items: [trip.name, trip.formattedDateRange])
             }
         }
+        .sheet(isPresented: $showProPaywall) {
+            PaywallView()
+        }
         .onAppear {
             checkIfSaved()
         }
@@ -523,6 +537,12 @@ struct TripDetailView: View {
     }
 
     private func saveTrip() {
+        // Check trip limit for free users
+        if !StoreManager.shared.isPro && savedTrips.count >= StoreManager.freeTripLimit {
+            showProPaywall = true
+            return
+        }
+
         guard let savedTrip = SavedTrip.from(trip, games: games, status: .planned) else {
             return
         }