feat(panel): add game UI registry and chess board component

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

panel/src/games/chess/index.ts

@@ -0,0 +1,9 @@
+import { gameUIRegistry } from "../registry";
+import { ChessBoard } from "./ChessBoard";
+
+gameUIRegistry.register({
+    slug: "chess",
+    name: "Chess",
+    icon: "♟",
+    component: ChessBoard,
+});