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/package.json

@@ -10,12 +10,10 @@
   },
   "dependencies": {
     "@imgly/background-removal": "^1.7.0",
-    "chess.js": "^1.4.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "lucide-react": "^0.564.0",
     "react": "^19.1.0",
-    "react-chessboard": "^5.10.0",
     "react-dom": "^19.1.0",
     "react-router-dom": "^7.13.2",
     "tailwind-merge": "^3.4.0",