add version to PDF

[egpbos]

Following #393, we should have the version somewhere in the PDF, preferably on the cover, but colofon or something is fine too.

[egpbos]

If we are working on this, perhaps we can also make sure this version gets uploaded to the Zenodo draft automatically. Both PDF generation and Zenodo upload are part of the same Actions workflow, so reusing the version info could make sense.