- Add internal mutex to Database struct with lock/unlock wrappers
- Add debug logging for lock acquisition and release with timing
- Wrap all write operations with database mutex
- Use _txlock=immediate in SQLite connection string
This works around apparent issues with SQLite's internal locking
not properly respecting busy_timeout in production environment.
- Add _txlock=immediate to SQLite connection string
- This prevents deadlocks by acquiring write locks at transaction start
- Multiple concurrent writers now queue properly instead of failing instantly
- Resolves 'database table is locked' errors in production
