- Add timezone_utils.py with system timezone auto-detection
- Configure venue timezone with system timezone as default fallback
- Update games_thread.py to use venue timezone for day calculations
- Update web dashboard API routes to use venue timezone for date filtering
- Add venue timezone configuration to web UI
- Fix day boundary issues where UTC midnight didn't match venue local time
- Ensure fixtures and bets are correctly associated with venue days

This resolves the problem where operations stored in UTC caused incorrect
day change calculations when midnight UTC didn't correspond to actual
midnight in the venue's timezone.