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/Core/Services/LocationService.swift

@@ -160,10 +160,10 @@ actor LocationService {
 
 // MARK: - Route Info
 
-struct RouteInfo: @unchecked Sendable {
+struct RouteInfo: Sendable {
     let distance: CLLocationDistance  // meters
     let expectedTravelTime: TimeInterval  // seconds
-    let polyline: MKPolyline?
+    nonisolated(unsafe) let polyline: MKPolyline?
 
     var distanceMiles: Double { distance * 0.000621371 }
     var travelTimeHours: Double { expectedTravelTime / 3600.0 }