fix: 22 audit fixes — concurrency, memory, performance, accessibility

- Move 7 Data(contentsOf:) calls off MainActor via Task.detached (BootstrapService)
- Batch-fetch N+1 queries in sync merge loops (CanonicalSyncService)
- Predicate-based gamesForTeam fetch instead of fetching all games (DataProvider)
- Proper Sendable on RouteInfo with nonisolated(unsafe) polyline (LocationService)
- [weak self] in BGTaskScheduler register closures (BackgroundSyncManager)
- Cache tripDays, routeWaypoints as @State with recompute (TripDetailView)
- Remove unused AnyCancellable, add Task lifecycle management (TripDetailView)
- Cache sportStadiums, recentVisits as stored properties (ProgressViewModel)
- Dynamic Type fonts replacing hardcoded sizes (OnboardingPaywallView)
- Accessibility labels/hints on stadium picker, date picker, map, stats,
  settings toggle, and day cards

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

SportsTime/Features/Paywall/Views/OnboardingPaywallView.swift

@@ -351,11 +351,11 @@ struct StadiumMapBackground: View {
             GeometryReader { geo in
                 HStack(spacing: 4) {
                     Text("6")
-                        .font(.system(size: 18, weight: .bold, design: .rounded))
+                        .font(.title3.bold())
                     Text("/")
-                        .font(.system(size: 14))
+                        .font(.subheadline)
                     Text("12")
-                        .font(.system(size: 14, weight: .medium, design: .rounded))
+                        .font(.subheadline.weight(.medium))
                 }
                 .foregroundStyle(color.opacity(0.25))
                 .padding(.horizontal, 12)