- Vision fetches NC preview at 640px via new sync helper.
- WORKER_THUMB_SIZES = set(); generate_thumbnails still does pHash.
- All medium.webp purged after verification.
- Bug: SECRET_KEY was missing from workers in compose, so
Fernet decrypt silently failed everywhere outside the backend
container. Phase 3 had been falling back to ExifTool the whole
time. Fix replicates SECRET_KEY to all worker services.
bb410eea49