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/CLAUDE.md

@@ -0,0 +1,31 @@
+# Panel (Admin Dashboard)
+
+## Stack
+- React 19 + React Router v7 + Tailwind CSS v4 (Vite plugin) + Lucide icons.
+- No component library (no Radix, no shadcn). All styling is inline Tailwind.
+- No external state management. All state via custom hooks (`useAuth`, `useUsers`, `useItems`, `useDashboard`, `useGameRoom`).
+
+## API Client
+- Thin `fetch` wrapper in `src/lib/api.ts` with typed generics: `get`, `post`, `put`, `del`.
+- Credentials: `same-origin` only — CORS requests will fail.
+- 401 responses redirect to Discord auth. No retry logic.
+- 204 / empty responses return `undefined`.
+
+## WebSocket
+- Singleton pattern in `useWebSocket()`. Global handler Set — multiple hooks share one connection.
+- Auto-reconnects with exponential backoff (max 30s).
+- `send()` and `subscribe()` API for components.
+
+## Patterns
+- **Draft editing:** Pages use `selectedUser → userDraft` flow. Changes aren't auto-saved. `saveDraft()` commits, `discardDraft()` reverts, `isDirty()` detects changes.
+- **Debounced search:** 300ms debounce on search inputs.
+- **No cache invalidation:** After mutations, manually call `refetch()` to update lists.
+
+## Routing
+- Role-based: player routes (`/dashboard`, `/games`, `/leaderboards`) and admin routes (`/admin/*`).
+- Sidebar auto-hides admin routes for non-admins.
+
+## Theme
+- Dark theme with "Celestial Gold" primary (`#e9c349`).
+- Semantic colors: destructive, success, warning, info.
+- 4-tier surface hierarchy. Utility: `cn()` from `clsx + tailwind-merge`.