Shit's fucked, it's going to take a few days to fix.
2021-09-23: shit's less fucked but expect a couple more days of downtime.
2021-09-24: uploaded files are being migrated to a new server, so until this process is done things are stalled.
2021-09-25: still migrating; but we're near the end of the process, so probably tomorrow things can move on.
2021-09-26: due to events outside my control and terrible ideas from the Danbooru developers, the site won't be available for a while still, probably a week or so.