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
                 }

SportsTime/Features/Progress/Views/ProgressTabView.swift

@@ -20,46 +20,19 @@ struct ProgressTabView: View {
 
     @Query private var visits: [StadiumVisit]
 
+    /// O(1) lookup for visits by ID (built from @Query results)
+    private var visitsById: [UUID: StadiumVisit] {
+        Dictionary(uniqueKeysWithValues: visits.map { ($0.id, $0) })
+    }
+
     var body: some View {
-        ScrollView {
-            VStack(spacing: Theme.Spacing.lg) {
-                // League Selector
-                leagueSelector
-                    .staggeredAnimation(index: 0)
-
-                // Progress Summary Card
-                progressSummaryCard
-                    .staggeredAnimation(index: 1)
-
-                // Map View
-                ProgressMapView(
-                    stadiums: viewModel.sportStadiums,
-                    visitStatus: viewModel.stadiumVisitStatus,
-                    selectedStadium: $selectedStadium
-                )
-                .frame(height: 300)
-                .clipShape(RoundedRectangle(cornerRadius: Theme.CornerRadius.large))
-                .overlay {
-                    RoundedRectangle(cornerRadius: Theme.CornerRadius.large)
-                        .stroke(Theme.surfaceGlow(colorScheme), lineWidth: 1)
-                }
-                .staggeredAnimation(index: 2)
-
-                // Stadium Lists
-                stadiumListsSection
-                    .staggeredAnimation(index: 3)
-
-                // Achievements Teaser
-                achievementsSection
-                    .staggeredAnimation(index: 4)
-
-                // Recent Visits
-                if !viewModel.recentVisits.isEmpty {
-                    recentVisitsSection
-                        .staggeredAnimation(index: 5)
-                }
+        Group {
+            if viewModel.stadiums.isEmpty {
+                ProgressView("Loading...")
+                    .frame(maxWidth: .infinity, maxHeight: .infinity)
+            } else {
+                scrollContent
             }
-            .padding(Theme.Spacing.md)
         }
         .themedBackground()
         .toolbar {
@@ -126,6 +99,51 @@ struct ProgressTabView: View {
         }
     }
 
+    // MARK: - Scroll Content
+
+    private var scrollContent: some View {
+        ScrollView {
+            VStack(spacing: Theme.Spacing.lg) {
+                // League Selector
+                leagueSelector
+                    .staggeredAnimation(index: 0)
+
+                // Progress Summary Card
+                progressSummaryCard
+                    .staggeredAnimation(index: 1)
+
+                // Map View
+                ProgressMapView(
+                    stadiums: viewModel.sportStadiums,
+                    visitStatus: viewModel.stadiumVisitStatus,
+                    selectedStadium: $selectedStadium
+                )
+                .frame(height: 300)
+                .clipShape(RoundedRectangle(cornerRadius: Theme.CornerRadius.large))
+                .overlay {
+                    RoundedRectangle(cornerRadius: Theme.CornerRadius.large)
+                        .stroke(Theme.surfaceGlow(colorScheme), lineWidth: 1)
+                }
+                .staggeredAnimation(index: 2)
+
+                // Stadium Lists
+                stadiumListsSection
+                    .staggeredAnimation(index: 3)
+
+                // Achievements Teaser
+                achievementsSection
+                    .staggeredAnimation(index: 4)
+
+                // Recent Visits
+                if !viewModel.recentVisits.isEmpty {
+                    recentVisitsSection
+                        .staggeredAnimation(index: 5)
+                }
+            }
+            .padding(Theme.Spacing.md)
+        }
+    }
+
     // MARK: - League Selector
 
     private var leagueSelector: some View {
@@ -385,7 +403,7 @@ struct ProgressTabView: View {
             }
 
             ForEach(viewModel.recentVisits) { visitSummary in
-                if let stadiumVisit = visits.first(where: { $0.id == visitSummary.id }) {
+                if let stadiumVisit = visitsById[visitSummary.id] {
                     NavigationLink {
                         VisitDetailView(visit: stadiumVisit, stadium: visitSummary.stadium)
                     } label: {