Design to eliminate UUID layer and use canonical IDs as the single
stadium/team/game identifier throughout the client. Key changes:
- Domain models use String IDs (canonical IDs)
- Remove UUID mapping dictionaries from DataProvider
- Simplify AchievementEngine (delete resolution helper)
- StadiumVisit uses single stadiumId field
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>