[PierreRaybaut]

Closes #521

Summary

doc/conf.py suppressed every docutils message (suppress_warnings = ["docutils"]), so reStructuredText errors went unnoticed, even in the strict gettext build (-W). The suppression was added for the duplicate substitution definitions of doc/index.rst and doc/intro/index.rst, defined once for HTML (64px) and once for LaTeX (1cm) in only:: blocks. These duplicates were actually not harmless: docutils keeps the last definition for every builder, before the only:: filtering, so the HTML pages used the LaTeX definitions. On the published site, the funders' logos and the operating mode icons are 1cm wide instead of 64px, get a white background in the dark theme, and the logos open the image instead of the CEA, CODRA and NLnet websites.

Without the suppression, these 6 duplicates were the only docutils errors left (title errors were fixed by #524).

Changes

• Fix: each image is defined once, with its HTML attributes and a latex-icon class; a doctree-resolved hook of doc/conf.py, size_latex_icons, sizes the images of this class to 1cm in the LaTeX output (the PDF is unchanged, except that the logos are now links)
• Build: docutils messages are no longer suppressed, with a comment warning against suppressing them or defining a substitution twice
• Documentation: release note entry (📖 Documentation, 1.4.1) and French translation

Validation

• Automated:
  • python -m sphinx build doc build/gettext -b gettext -W -E (the CI command) fails with the suppression removed and the duplicates kept (6 "Duplicate substitution definition name" errors), and succeeds with the fix
  • HTML (en, fr) and LaTeX builds with no warning at all
  • HTML: logos and icons at 64px with the dark-light class, logos linking to their websites; LaTeX: \sphinxincludegraphics[width=1cm] for the same images
  • Ruff clean on doc/conf.py
• Manual: home page and Getting started page checked in English and French, light and dark themes, and the release note entry

Out of scope

• Pull request CI does not build the documentation #535: pull request CI does not build the documentation, so such errors are only caught by pages.yml, release builds or local builds
• Card icons missing in the French documentation #536: card icons missing in the French documentation (pre-existing, also on the published site)

Release note: entry in the 📖 Documentation section of DataLab 1.4.1. This PR targets release (1.4.1 maintenance line); the commit will be cherry-picked into develop.

Assisted-by: Claude Opus 5.5