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/Export/PDFGenerator.swift

@@ -103,7 +103,7 @@ final class PDFGenerator {
             .foregroundColor: UIColor.black
         ]
         let titleRect = CGRect(x: margin, y: y, width: contentWidth, height: 50)
-        (trip.name as NSString).draw(in: titleRect, withAttributes: titleAttributes)
+        (trip.displayName as NSString).draw(in: titleRect, withAttributes: titleAttributes)
         y += 55
 
         // Date range