fix: restrict By Route wizard to stadium cities and filter sports by selected cities

LocationSearchSheet now shows only stadium cities (with sport badges) when
selecting start/end locations, preventing users from picking cities with no
stadiums. TripWizardViewModel filters available sports to the union of sports
at the selected cities, and clears invalid selections when locations change.

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

SportsTime/Features/Trip/Views/Wizard/TripWizardView.swift

@@ -60,6 +60,12 @@ struct TripWizardView: View {
                                     startLocation: $viewModel.startLocation,
                                     endLocation: $viewModel.endLocation
                                 )
+                                .onChange(of: viewModel.startLocation) { _, _ in
+                                    viewModel.validateSportsForLocations()
+                                }
+                                .onChange(of: viewModel.endLocation) { _, _ in
+                                    viewModel.validateSportsForLocations()
+                                }
                             }
 
                             if viewModel.showTeamFirstStep {