JATS skips figure images with a file URI source #5016

Follow-up to #4912 and the maintainer’s comment:
#4912 (comment)

With a JATS DocumentStream, relative figure images are skipped when source_uri is a file URI, even with fetch_images=True and enable_local_fetch=True. The equivalent Path source loads the image.

Expected: supported local file URI sources should load relative figures while preserving permissions and directory confinement.

The follow-up also covers rejecting non-localhost file URI authorities outside Windows and preserving article content when a truncated image fails to decode.

Verified on main at 90234a7. A fix and regression tests are ready.