suggestion: Add a .nvmrc file to root

[coliff]

Currently there are 5x GitHub Actions workflows which specify using NODE: 24.

Instead, to store the Node version in a single place we could add a .nvmrc file to the project root and reference that.

e.g.

      - name: Setup Node.js
        uses: actions/setup-node@48b55a011bda9f5d6aeb4c2d9c7362e8dae4041e # v6.4.0
        with:
          node-version-file: ".nvmrc"
          cache: npm

Then, when ready to switch to Node 26 it only needs to be updated in a single place.

As a bonus, it'd also mean folks contributing to Bootstrap who are using nvm will also use the same recommended Node version for development.

Happy to make a PR if you'd like.