For the record, a cookie is kept on each machine that keeps a count of times you visit git.sr.ht and hg.sr.ht, and whichever one has more visits is displayed on the navbar.

~ociaw's solution looks like a good one to me. If not that, then at least put it in the navbar. I don't think anyone is going to be particularly confused by hg's presence, since it wouldn't be overriding git.

I'm willing to help work on this issue once I get familiar with the sr.ht codebase. There are Python libraries to make implementing WebAuthn easier. Perhaps the WebAuthn pages could have notices saying "JavaScript is needed on this page for WebAuthn functionality and nothing else" or something like that.