The lightbox falls back to photo.url (the ORIGINAL) when preview_url is null,
which happens by default (lightbox_preview_enabled=false). For HEIC/HEIF/DNG the
original bytes aren't renderable in an <img>, so the lightbox showed a broken
image. Now force preview_url for those formats (by MIME or extension) regardless
of the toggle, so the browser always gets the generated JPEG preview. Covers DNG
too (forward-compatible with #833).
EXPERIMENTAL caveat unchanged: whether the preview actually renders still depends
on the backend decoding the source — HEVC-in-HEIC on the prod Alpine image is
unverified, DNG needs exiftool (#833). Documented on the PR.
Paul Nothaft
808d305549