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/Services/SuggestedTripsGenerator.swift

@@ -584,7 +584,7 @@ final class SuggestedTripsGenerator {
         if cities.count <= 1 {
             return cities.first ?? "Road Trip"
         }
-        return cities.joined(separator: " - ")
+        return cities.joined(separator: " → ")
     }
 
     // MARK: - Corridor Trip Building