Discarded photos now look discarded in the grid (50% opacity + grayscale)
with a red trash badge in the corner instead of a bare icon. The discard
action bar gains a "Delete N" button that permanently deletes only the
current selection, complementing the existing "Empty discard pile".
Backend: new DELETE /discard endpoint accepting {photo_ids: [...]} that
permanently removes only listed photos. Skips ids that aren't in the
discard pile so it can never bypass the soft-delete safety net.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>