refactor(games): rework room lifecycle events and remove chess plugin

Consolidate room leave/delete event handling into RoomManager emitter,
remove redundant PLAYER_LEFT publishes from GameServer, and delete the
chess game plugin (board, types, tests) in favor of the new plugin
architecture. Add per-module CLAUDE.md files for leveling, guild-settings,
feature-flags, db, api, and panel to improve agent navigability.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

panel/src/games/GameRoom.tsx

@@ -3,7 +3,6 @@ import { useParams, useNavigate, useLocation } from "react-router-dom";
 import { useGameRoom } from "../lib/useGameRoom";
 import { gameUIRegistry } from "./registry";
 import { Loader2 } from "lucide-react";
-import "./chess";
 
 function CopyInviteLink({ url }: { url: string }) {
     const [copied, setCopied] = useState(false);