refactor: change domain model IDs from UUID to String canonical IDs

This refactor fixes the achievement system by using stable canonical string
IDs (e.g., "stadium_mlb_fenway_park") instead of random UUIDs. This ensures
stadium mappings for achievements are consistent across app launches and
CloudKit sync operations.

Changes:
- Stadium, Team, Game: id property changed from UUID to String
- Trip, TripStop, TripPreferences: updated to use String IDs for games/stadiums
- CKModels: removed UUID parsing, use canonical IDs directly
- AchievementEngine: now matches against canonical stadium IDs
- All test files updated to use String IDs instead of UUID()

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

SportsTime/Export/Services/PDFAssetPrefetcher.swift

@@ -15,8 +15,8 @@ actor PDFAssetPrefetcher {
     struct PrefetchedAssets {
         let routeMap: UIImage?
         let cityMaps: [String: UIImage]
-        let teamLogos: [UUID: UIImage]
-        let stadiumPhotos: [UUID: UIImage]
+        let teamLogos: [String: UIImage]
+        let stadiumPhotos: [String: UIImage]
         let cityPOIs: [String: [POISearchService.POI]]
 
         var isEmpty: Bool {
@@ -63,7 +63,7 @@ actor PDFAssetPrefetcher {
     /// - Returns: All prefetched assets
     func prefetchAssets(
         for trip: Trip,
-        games: [UUID: RichGame],
+        games: [String: RichGame],
         progressCallback: ((PrefetchProgress) async -> Void)? = nil
     ) async -> PrefetchedAssets {
         var progress = PrefetchProgress()
@@ -71,8 +71,8 @@ actor PDFAssetPrefetcher {
         // Collect unique teams and stadiums from games
         var teams: [Team] = []
         var stadiums: [Stadium] = []
-        var seenTeamIds: Set<UUID> = []
-        var seenStadiumIds: Set<UUID> = []
+        var seenTeamIds: Set<String> = []
+        var seenStadiumIds: Set<String> = []
 
         for (_, richGame) in games {
             if !seenTeamIds.contains(richGame.homeTeam.id) {