add engines field

.npmrc

···
+engine-strict=true

package-lock.json

···
         "prettier": "^3.0.0",
         "tsx": "^3.12.7",
         "typescript": "^5.0.4"
+      },
+      "engines": {
+        "node": ">=18.14"
       }
     },
     "node_modules/@clack/core": {

package.json

···
     "test": "tsx ./quartz/util/path.test.ts",
     "profile": "0x -D prof ./quartz/bootstrap-cli.mjs build --concurrency=1"
   },
+  "engines": {
+    "node": ">=18.14"
+  },
   "keywords": [
     "site generator",
     "ssg",