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/Features/Progress/Views/StadiumVisitSheet.swift

@@ -389,8 +389,7 @@ struct StadiumVisitSheet: View {
 
         // Create the visit
         let visit = StadiumVisit(
-            canonicalStadiumId: stadium.id.uuidString, // Simplified - in production use StadiumIdentityService
-            stadiumUUID: stadium.id,
+            stadiumId: stadium.id,
             stadiumNameAtVisit: stadium.name,
             visitDate: visitDate,
             sport: selectedSport,