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>

package.json

@@ -40,7 +40,6 @@
   },
   "dependencies": {
     "@napi-rs/canvas": "^0.1.89",
-    "chess.js": "^1.4.0",
     "discord.js": "^14.25.1",
     "dotenv": "^17.2.3",
     "drizzle-orm": "^0.44.7",