perf: optimize Progress tab with O(1) lookups and loading state

Replace O(n) linear searches with dictionary lookups in ProgressViewModel
and ProgressTabView. Add loading spinner while data loads.

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

SportsTime/Features/Progress/ViewModels/ProgressViewModel.swift

@@ -16,7 +16,7 @@ final class ProgressViewModel {
     // MARK: - State
 
     var selectedSport: Sport = .mlb
-    var isLoading = false
+    var isLoading = true
     var error: Error?
     var errorMessage: String?
 
@@ -42,10 +42,8 @@ final class ProgressViewModel {
             visits
                 .filter { $0.sportEnum == selectedSport }
                 .compactMap { visit -> String? in
-                    // Match visit's canonical stadium ID to a stadium
-                    stadiums.first { stadium in
-                        stadium.id == visit.stadiumId
-                    }?.id
+                    // O(1) dictionary lookup via DataProvider
+                    dataProvider.stadium(for: visit.stadiumId)?.id
                 }
         )
 
@@ -120,7 +118,7 @@ final class ProgressViewModel {
             .sorted { $0.visitDate > $1.visitDate }
             .prefix(10)
             .compactMap { visit -> VisitSummary? in
-                guard let stadium = stadiums.first(where: { $0.id == visit.stadiumId }),
+                guard let stadium = dataProvider.stadium(for: visit.stadiumId),
                       let sport = visit.sportEnum else {
                     return nil
                 }