Specify node version in `package.json`

[jbampton]

While updating the Node.js version in the documentation is a good step, this requirement is not programmatically enforced. To prevent potential build issues for contributors using an incompatible Node.js version, it's a best practice to also specify this requirement in package.json using the engines field.

Consider adding the following to your package.json:

"engines": {
  "node": ">=20.x"
}

This will cause package managers like npm and yarn to produce a warning or error if a developer is using an unsupported version of Node.js, ensuring a more consistent and stable development environment.

Originally posted by @gemini-code-assist[bot] in #366 (comment)