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/Polls/Views/PollDetailView.swift

@@ -274,7 +274,7 @@ struct PollDetailView: View {
                     let rank = results.tripScores.firstIndex { $0.tripIndex == item.tripIndex }! + 1
                     ResultRow(
                         rank: rank,
-                        tripName: trip.name,
+                        tripName: trip.displayName,
                         score: item.score,
                         percentage: results.scorePercentage(for: item.tripIndex),
                         isLeader: rank == 1 && item.score > 0
@@ -420,7 +420,7 @@ private struct TripPreviewCard: View {
                         .background(Theme.warmOrange)
                         .clipShape(Capsule())
 
-                    Text(trip.name)
+                    Text(trip.displayName)
                         .font(.headline)
                         .foregroundStyle(.primary)
                 }
@@ -441,12 +441,6 @@ private struct TripPreviewCard: View {
                 }
                 .font(.caption)
                 .foregroundStyle(.secondary)
-
-                // Show cities
-                Text(trip.stops.map { $0.city }.joined(separator: " → "))
-                    .font(.caption)
-                    .foregroundStyle(.secondary)
-                    .lineLimit(2)
             }
 
             Image(systemName: "chevron.right")