V239 - FORCE ARBITRATION WHEN A PLAYER LEAVES

- Keeps V238 LAN/direct-IP and persistent account-bound slot behavior.
- When any remote player leaves an active multiplayer game, the HOST is forced
  back to the Multiplayer Arbitration screen.
- The departed player's live character is removed only after the arbitration
  screen becomes active, which makes deletion occur in the proper BG2 screen.
- The departed account keeps its reserved account-bound slot.
- Other accounts cannot take that reserved slot.
- Reconnecting with the same account reclaims the same slot.
- No CHR/BIO deletion, no backups, and no automatic character restoration.
