* feat: add /ban command to blacklist users
- Create 'blacklist' table in database to store banned user IDs.
- Implement handle_ban to blacklist users by replying to their messages.
- Add check in handle_message to intercept messages from banned users.
* feat: add /unban command to restore user communication
- Implement handle_unban to remove user IDs from the blacklist.
- Allow admins to restore communication by replying to historic
messages.
* docs: update README.md