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/Paywall/ViewModifiers/ProGate.swift

@@ -0,0 +1,71 @@
+//
+//  ProGate.swift
+//  SportsTime
+//
+//  View modifier that gates Pro-only features.
+//
+
+import SwiftUI
+
+struct ProGateModifier: ViewModifier {
+    let feature: ProFeature
+
+    @State private var showPaywall = false
+
+    func body(content: Content) -> some View {
+        content
+            .onTapGesture {
+                if !StoreManager.shared.isPro {
+                    showPaywall = true
+                }
+            }
+            .allowsHitTesting(!StoreManager.shared.isPro ? true : true)
+            .overlay {
+                if !StoreManager.shared.isPro {
+                    Color.clear
+                        .contentShape(Rectangle())
+                        .onTapGesture {
+                            showPaywall = true
+                        }
+                }
+            }
+            .sheet(isPresented: $showPaywall) {
+                PaywallView()
+            }
+    }
+}
+
+/// Modifier for buttons that should show paywall when tapped by free users
+struct ProGateButtonModifier: ViewModifier {
+    let feature: ProFeature
+    let action: () -> Void
+
+    @State private var showPaywall = false
+
+    func body(content: Content) -> some View {
+        Button {
+            if StoreManager.shared.isPro {
+                action()
+            } else {
+                showPaywall = true
+            }
+        } label: {
+            content
+        }
+        .sheet(isPresented: $showPaywall) {
+            PaywallView()
+        }
+    }
+}
+
+extension View {
+    /// Gates entire view - tapping shows paywall if not Pro
+    func proGate(feature: ProFeature) -> some View {
+        modifier(ProGateModifier(feature: feature))
+    }
+
+    /// Gates a button action - shows paywall instead of performing action if not Pro
+    func proGateButton(feature: ProFeature, action: @escaping () -> Void) -> some View {
+        modifier(ProGateButtonModifier(feature: feature, action: action))
+    }
+}