Also return URL as part of work/tags/series and other fetches

It would be nice if we returned URLs as part of the work/tag/series details (or anywhere possible). While it's true that you can easily get it by using the `/urls` utilities, that's less discoverale and it's a common-enough need that it might just be worth sticking it in there.

This may be even more useful with multi-archive. The fact that it would save me time debugging tests, and also that it might have helped me figure out why a test was broken only has a liiiiittle bit to do with it.