Implements a complete alias system allowing players to create command shortcuts.
Aliases are expanded during dispatch with a recursion guard (max 10 levels).
Changes:
- Add aliases field to Player dataclass (dict[str, str])
- Add player_aliases table to database schema
- Add save_aliases() and load_aliases() persistence functions
- Add alias/unalias commands with built-in command protection
- Integrate alias expansion into dispatch() before command resolution
- Add comprehensive test coverage for all features
