fix: standardize trip name display with arrow separators app-wide

- Add `displayName` computed property to Trip model that always
  generates city list with " → " separator for consistent display
- Replace all `trip.name` usages with `trip.displayName` in UI files
- Update SuggestedTripsGenerator to use " → " separator
- Update PDFGenerator to use displayName for PDF titles

This ensures all trip names display consistently regardless of when
the trip was created or how the name was originally stored.

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

SportsTime/Features/Home/Views/HomeView.swift

@@ -329,7 +329,7 @@ struct SavedTripCard: View {
                 }
 
                 VStack(alignment: .leading, spacing: 4) {
-                    Text(trip.name)
+                    Text(trip.displayName)
                         .font(.body)
                         .foregroundStyle(Theme.textPrimary(colorScheme))
 
@@ -653,7 +653,7 @@ struct SavedTripListRow: View {
             .frame(width: 20)
 
             VStack(alignment: .leading, spacing: Theme.Spacing.xs) {
-                Text(trip.name)
+                Text(trip.displayName)
                     .font(.headline)
                     .foregroundStyle(Theme.textPrimary(colorScheme))