Trashing a page hides it from viewers everywhere except the image
endpoints: images.getAssetUrl and images.listForStrategy counted a
reference on a trashed page like any other, so a viewer, including one who
joined after the delete, could still list and fetch those images.

For a reader below editor both now count only references on pages outside
the trash. Editors, who can restore the page, see its images as before, and
the reclaim and stale-upload checks keep counting trashed pages.