- Remap 129 broken image paths in v1/en_chapters to the files that exist
under v1/img (old chapter numbering, renamed files, and .pdf figures
that browsers cannot display inline).
- Restore ch07/7.5/distribute.png and ch08/distillation.png, which were
dropped in #499 because the `dist*` .gitignore rule matched them;
narrow the rule to `/dist/`.
- Fix the English toc blocks: chapter entries now point at real files and
the root toc has part headings, so section pages are built again
(previously only chapter index pages were generated).
- Add tests/test_image_references.py to CI to catch missing or
unrenderable figure references.
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
