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/Progress/Views/StadiumVisitSheet.swift

@@ -114,6 +114,8 @@ struct StadiumVisitSheet: View {
                                 .foregroundStyle(Theme.textMuted(colorScheme))
                         }
                     }
+                    .accessibilityLabel(selectedStadium != nil ? "Stadium: \(selectedStadium!.name)" : "Select stadium")
+                    .accessibilityHint("Opens stadium picker")
                 } header: {
                     Text("Location")
                 }
@@ -122,6 +124,7 @@ struct StadiumVisitSheet: View {
                 // Visit Details Section
                 Section {
                     DatePicker("Date", selection: $visitDate, displayedComponents: .date)
+                        .accessibilityHint("Select the date you visited this stadium")
 
                     Picker("Visit Type", selection: $visitType) {
                         ForEach(VisitType.allCases, id: \.self) { type in