fix: 14 audit fixes — concurrency, memory, performance, accessibility

Second audit round addressing data races, task stacking, unbounded
caches, and VoiceOver gaps across 7 files.

Concurrency:
- Move NSItemProvider @State access into MainActor block (3 drop handlers)
- Cancel stale ScheduleViewModel tasks on rapid filter changes

Memory:
- Replace unbounded image dict with LRUCache(countLimit: 50)
- Replace demo-mode asyncAfter with cancellable Task

Performance:
- Wrap debug NBA print() in #if DEBUG
- Cache visitsById via @State + onChange instead of per-render computed
- Pre-compute sportProgressFractions in ProgressViewModel
- Replace allGames computed property with hasGames bool check
- Cache sortedTrips via @State + onChange in SavedTripsListView

Accessibility:
- Add combined VoiceOver label to progress ring
- Combine away/home team text into single readable phrase
- Hide decorative StadiumDetailSheet icon from VoiceOver
- Add explicit accessibilityLabel to SportFilterChip
- Add combined accessibilityLabel to GameRowView

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

SportsTime/Features/Progress/ViewModels/ProgressViewModel.swift

@@ -46,6 +46,9 @@ final class ProgressViewModel {
     /// Unvisited stadiums for the selected sport
     private(set) var unvisitedStadiums: [Stadium] = []
 
+    /// Pre-computed progress fractions per sport (avoids filtering visits per sport per render)
+    private(set) var sportProgressFractions: [Sport: Double] = [:]
+
     /// Stadiums for the selected sport
     var sportStadiums: [Stadium] {
         stadiums.filter { $0.sport == selectedSport }
@@ -200,6 +203,19 @@ final class ProgressViewModel {
             }
         }
         stadiumVisitStatus = statusMap
+
+        // Pre-compute sport progress fractions for SportSelectorGrid
+        var sportCounts: [Sport: Int] = [:]
+        for visit in visits {
+            if let sport = visit.sportEnum {
+                sportCounts[sport, default: 0] += 1
+            }
+        }
+        sportProgressFractions = Dictionary(uniqueKeysWithValues: Sport.supported.map { sport in
+            let total = LeagueStructure.stadiumCount(for: sport)
+            let visited = min(sportCounts[sport] ?? 0, total)
+            return (sport, total > 0 ? Double(visited) / Double(total) : 0)
+        })
     }
 
     // MARK: - Progress Card Generation