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/Core/Models/Domain/Trip.swift

@@ -70,6 +70,13 @@ struct Trip: Identifiable, Codable, Hashable {
             return stop.city
         }
     }
+
+    /// Display name generated from cities - always uses " → " separator for consistency
+    var displayName: String {
+        let cityList = cities
+        return cityList.isEmpty ? name : cityList.joined(separator: " → ")
+    }
+
     var uniqueSports: Set<Sport> { preferences.sports }
     var startDate: Date { stops.first?.arrivalDate ?? preferences.startDate }
     var endDate: Date { stops.last?.departureDate ?? preferences.endDate }