Return better error messages when images are not found to help diagnose the problem faster

[mihow]

Currently if an image is a local URL or any bad URL it returns a generic 500 error. A user data error (400) with details about the failing image would be much more helpful. There's also a chance more details are being returned with the 500 error but Antenna is not displaying them.

Example from the logs:

2025-08-09 01:26:21 [info     ] Downloading http://django:8000/media/example_captures/19/black-witch-moth-20231112123850-snapshot.jpeg to /tmp/ami_imagesbm3gmspn/black-witch-moth-20231112123850-snapshot.jpeg
INFO:     192.168.123.178:35684 - "POST /process HTTP/1.1" 500 Internal Server Error

[mihow]

@carlosgjs while you are deep in the PyTorch code in the processing service, this may be something you have thoughts about. How can we "bubble up" more helpful exceptions all the way to the Antenna frontend (through the processing service API)?