feat: mark playground package as private to exclude from publishing

Author: Disturbing

packages/playground/package.json

@@ -1,7 +1,7 @@
 {
   "name": "@nullshot/playground",
   "version": "0.2.3",
-  "private": false,
+  "private": true,
   "main": "./dist/index.js",
   "module": "./dist/index.mjs",
   "types": "./dist/index.d.ts",