For a single card card, see ability to completely delete a card
currently at admin/empty_trash (must have admin priveleges).
Nice. Does it ask for confirmation before doing it?
(and does it actually delete old files/images?)
no on both of those. so I wouldn't advise linking to it.
basically anything that starts with "/admin/" is temporary and will have a new address once we can do it properly with card actions. The current implementation is bare bones, and I don't expect to build any pretty interface around it. Once we're doing it in a more permanent way, that will change.
The files issue is definitely worth ticketing, though. delete trashed files when emptying trash