feature: match chat archive and chat log

[lukepolo]

Keeps a capped 7-day archive of every match and team chat line so staff can review a match after its live rooms expire.

• Every Match and MatchTeam line, from the web or the game, is copied to chat:archive:<matchId>, capped at 5000 lines, 8 MB and 16 KB per line, and flagged when cut short
• The archive expires a week after the match ends and is deleted with its match; restarting a match slides the expiry again
• Edits are rate limited, applied once and in order, and keep the original text plus the last four versions; deletes keep the line and who deleted it
• New GET /chat/matches/:matchId/log for match organizers and above, by their current role, once a match has ended; anyone who took part gets all chat only
• Archive failures never affect sending, editing, deleting or draft moves, and the archive is never served over the websocket

From DEAFCS: DEAFCS/api-deafcs@ce8576c1