fix(duel): dispose bot duelists in place to stop ghost entities blanking login screens

EndDuel teleported bot participants back to Twin City before disposing them. When the bot was already disposed (null DBClient), the teleport re-added it to map 1002 and threw inside Vision.Check, skipping the dispose. The ghost then crashed Vision.Check for every player spawning near 432,378, leaving an empty screen on login.

Bots now leave duels by disposing in place, and Vision.Check skips players and bots without a DBClient.