The rate limiter caps new connections (10/min/IP) and game starts (15/min/IP),
but one IP could still hold open unbounded sockets by trickling them in under
the connection rate and keeping them alive — hoarding spectator slots and
server resources ahead of a public launch.
Track live sockets per IP in ConnectionHandler and reject new ones past a cap
(MAX_SOCKETS_PER_IP, default 10). Slots are freed on disconnect and reconciled
against live sockets in the periodic cleanup so a missed disconnect can't
wrongly lock out an IP.
