Update to latest Node v20.x patch (or upgrade to Node v22 or v24)

We're a few patch versions behind on v20.x — review the changelog, check for an updated Docker image, and update:

https://nodejs.org/en/about/previous-releases
https://endoflife.date/nodejs

We could also consider jumping up to Node v22.x or v24.x, both of which are LTS versions. (Node v20 support ends Apr 2026, so we'll need to make the move sometime before spring.)