v0.7.3

Veto lobby presence.

- A player joining a match lobby now receives a snapshot of who is really there (both teams with a connected flag, the spectator count, and the veto session), built after they join. Before, the snapshot was hard-coded to nobody, so an opponent already in the lobby showed as absent.
- Presence is counted per team, not per socket: a second tab or a reconnect that overlaps the old socket's teardown no longer flaps a present team to absent.
- Lobby teardown is atomic with joins, so two people in one match can no longer land in two lobbies.
- A socket that stops answering pings for 90 s is dropped instead of lingering as connected.

Includes v0.7.2 (archived leagues hidden from a player's own lists; team season stats).

Pull request: https://github.com/mtottenh/cg/pull/16