Add explicit Node.js engine requirement to package.json

### Describe the solution you'd like

The repository currently defines Node.js tooling through `.nvmrc` and package manager configuration, but does not expose an explicit `engines.node` requirement inside `package.json`.

Adding an `engines` field would improve contributor onboarding, reduce environment inconsistencies, and make Node.js version expectations clearer for local development and CI environments.

Example:

```json
"engines": {
"node": ">=22"
}