Gitea user auto-purging

I had to reinstate auto-purging of git.tt-rss.org user accounts because of overwhelming bot registrations (366 users removed right now) despite cloudflare bot-checks and whatnot.

I’m not going to describe exact criteria used (other than “this account seemingly wasn’t helping with development of stuff”) but I hope no legit accounts were affected. If yours was and you feel it was wrong, tell me about it.