helps mastodon frontend and apps have better context:
https://mastodon.social/users/Gargron/statuses/100101267352899379

Should also use indexes better.

Also, use specialized functions to get safe data.

fixes #175

multi-field @> comparison is very expensive, so only use @> for the field where it matters
this makes the query take only a few usec to execute verses many msec on a busy instance

This crashed Mastodon workers.

activitypub controller: note that the HTTP Host header must be forwarded for http signature validation to work