Show version information in modal

The user can see the version of Central they're using by clicking Version in the help dropdown in the navbar. That opens version.txt in a new tab. Rather than opening a new tab, I think it'd be nicer to show the version information in a modal.

Now that getodk/central-frontend#1094 is in place, it'd also be easy to show the short version tag (e.g., v2024.3.0). Frontend now parses that from version.txt. I think it'd be nice to highlight the short version tag while still showing the whole of version.txt in case those details are needed.