Auto-call /result after song start #2

When a match starts, automatically call /result as an ephemeral message that pings the referee who started the match.

We need to track which referee initiated the match for this purpose.

Acceptance criteria:

• /result is called automatically when a song starts
• Message is ephemeral (if possible, we only want the referee to see this)
• Pings the referee who started the match
• Referee tracking is persisted per match