chore: standardize on Node 24 (#9521)

## Summary

Standardize the repo's Node contract on 24 while centralizing workflow
resolution through `.nvmrc` so local setup, CI, and package metadata
stay aligned from one version file.

## Changes

- **What**: Add `package.json` `engines.node = 24.x`, switch every
`actions/setup-node` workflow in the repo to `node-version-file:
'.nvmrc'`, and update contributor and Playwright docs to point to
`.nvmrc` as the Node source of truth.

## Review Focus

The workflow behavior should be unchanged apart from sourcing the Node
version from `.nvmrc` instead of repeating literals like `20`, `22`,
`24.x`, or `lts/*`. GitHub's formatter also moved the new `engines`
block to the package metadata section near the end of `package.json`.

---------

Co-authored-by: GitHub Action <action@github.com>
Co-authored-by: Alexander Brown <drjkl@comfy.org>

.github/workflows/release-draft-create.yaml

@@ -26,7 +26,7 @@ jobs:
           version: 10
       - uses: actions/setup-node@v6
         with:
-          node-version: 'lts/*'
+          node-version-file: '.nvmrc'
           cache: 'pnpm'
 
       - name: Get current version