When ImageMagick fails to process an uploaded image (e.g., corrupted PNG
with invalid IHDR data), the backend was raising :type :internal with
:code :imagemagick-error, which mapped to HTTP 500. The frontend treated
this as a server error and displayed the full error page.
Changed exec-magick! to raise :type :validation with :code :invalid-image
instead. This flows through the existing :invalid-image handler in
errors.clj which returns HTTP 400. The frontend's handle-media-error and
process-error now catch this code and show a notification banner.
AI-assisted-by: qwen3.7-plus
26c4ec18fe