add a /stop command (referee-only) that forcefully cancels an in-progress match. should use autocomplete to select from currently active matches (matchId + player names). should show an ephemeral confirmation prompt before actually stopping.
when confirmed:
- add an 'abandoned' status alongside the existing 'completed' status in the match schema
- save the match to DB with status 'abandoned' and a completedAt timestamp, preserving the audit trail of what was played so far
- stop any active collector (session.activeCollector) so dangling ban/pick/ready listeners don't fire
- broadcast a match.abandoned WS event so the overlay clears
- call clearMatchSession() + resetMatchState()
implemtnted yay