U2Net only ever downloaded lazily on the first Remove Background click,
unlike SAM which retries on every container start. If that one attempt
failed (DNS/firewall) the model was never fetched again, surfacing as
"No background removal method available. Install u2net or rembg."
Mirrors the existing SAM auto-download/AUTO_DOWNLOAD_SAM pattern for
U2Net, and documents manual host-side recovery in the README.
Also deletes backend/app/services/u2net_model.py (hand-written
U2NET/U2NETP PyTorch classes) — unused since tools.py switched to
cv2.dnn.readNetFromONNX for background removal.
Claude
a4a9dbc33a