feat: add sliding window trip generation for By Games mode

Adds a trip duration stepper (2-21 days) to the By Games planning mode.
When users select specific games, the planner now generates ALL possible
N-day windows containing those games (e.g., 7-day trips starting on
different days), finding additional games in each window to maximize
route options.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Features/Trip/Views/TripCreationView.swift

@@ -66,9 +66,10 @@ struct TripCreationView: View {
                         datesSection
 
                     case .gameFirst:
-                        // Sports + Game Picker
+                        // Sports + Game Picker + Trip Duration
                         sportsSection
                         gameBrowserSection
+                        tripDurationSection
 
                     case .locations:
                         // Locations + Sports + optional games
@@ -512,6 +513,39 @@ struct TripCreationView: View {
         }
     }
 
+    private var tripDurationSection: some View {
+        ThemedSection(title: "Trip Duration") {
+            VStack(alignment: .leading, spacing: Theme.Spacing.sm) {
+                HStack {
+                    Image(systemName: "calendar.badge.clock")
+                        .foregroundStyle(Theme.warmOrange)
+                    Text("Days")
+                        .font(.body)
+                        .foregroundStyle(Theme.textPrimary(colorScheme))
+
+                    Spacer()
+
+                    Stepper(
+                        value: $viewModel.gameFirstTripDuration,
+                        in: 2...21,
+                        step: 1
+                    ) {
+                        Text("\(viewModel.gameFirstTripDuration) days")
+                            .font(.body.monospacedDigit())
+                            .foregroundStyle(Theme.textPrimary(colorScheme))
+                    }
+                }
+                .padding(Theme.Spacing.md)
+                .background(Theme.cardBackgroundElevated(colorScheme))
+                .clipShape(RoundedRectangle(cornerRadius: Theme.CornerRadius.medium))
+
+                Text("We'll find all possible \(viewModel.gameFirstTripDuration)-day trips that include your selected games")
+                    .font(.caption)
+                    .foregroundStyle(Theme.textSecondary(colorScheme))
+            }
+        }
+    }
+
     private var sportsSection: some View {
         ThemedSection(title: "Sports") {
             SportSelectorGrid(
@@ -1406,6 +1440,7 @@ struct LocationSearchSheet: View {
 
 enum TripSortOption: String, CaseIterable, Identifiable {
     case recommended = "Recommended"
+    case mostCities = "Most Cities"
     case mostGames = "Most Games"
     case leastGames = "Least Games"
     case mostMiles = "Most Miles"
@@ -1417,6 +1452,7 @@ enum TripSortOption: String, CaseIterable, Identifiable {
     var icon: String {
         switch self {
         case .recommended: return "star.fill"
+        case .mostCities: return "mappin.and.ellipse"
         case .mostGames, .leastGames: return "sportscourt"
         case .mostMiles, .leastMiles: return "road.lanes"
         case .bestEfficiency: return "gauge.with.dots.needle.33percent"
@@ -1514,6 +1550,8 @@ struct TripOptionsView: View {
         switch sortOption {
         case .recommended:
             return filtered
+        case .mostCities:
+            return filtered.sorted { $0.stops.count > $1.stops.count }
         case .mostGames:
             return filtered.sorted { $0.totalGames > $1.totalGames }
         case .leastGames: