fix: Add engines field to require Node.js 20+ for Astro 5.x compatibility

Astro 5.x requires Node.js >=18.20.8, added engines field to ensure
Nixpacks/Easypanel uses Node.js 20 instead of defaulting to 18.20.5

package.json

@@ -2,6 +2,9 @@
   "name": "moreminimore-redesign",
   "type": "module",
   "version": "0.0.1",
+  "engines": {
+    "node": ">=20.0.0"
+  },
   "scripts": {
     "dev": "astro dev",
     "build": "astro build",