docs: upgrade Quarto 1.6.26 → 1.9.37

[elnelson575]

Summary

• Bumps Quarto version in CI from `1.6.26` to `1.9.37`
• Enables `llms-txt: true` in `_quarto.yml` (new in 1.9 — generates `llms.txt` + `.llms.md` files alongside HTML pages for LLM-friendly content)
• Adds `**/*.quarto_ipynb` to `docs/.gitignore` (Quarto 1.8 now creates these as intermediate files; 1.8 also adds them to `.gitignore` by default in new projects, so this is consistent with that change)
• Updates `sidebar.yml` with entries for recently added APIs (`tool_web_search`, `tool_web_fetch`, `parallel_chat*`, `AssistantTurn`/`UserTurn`/`SystemTurn`, new content types)
• Adds explicit `render:` list to `_quarto.yml` to ensure all pages are rendered by Quarto 1.9 (previously auto-discovered)
• Adds `CHANGELOG.md` to render list (was missing, causing broken Changelog link in navbar)
• Adds `tests/compare-sites/` — a Playwright + Claude vision script for comparing two builds of the docs site page-by-page

Breaking change analysis: Quarto 1.6.26 → 1.9.37

Reviewed the changelogs for 1.7, 1.8, and 1.9.
No breaking changes affect this site.

Details

1.7 — No impact

• Mostly regression fixes and non-HTML format changes (PDF/LaTeX template changes, Typst, Beamer)
• The one notable breaking change (`common.latex` now uses `pandoc.tex` partial) only affects custom LaTeX template authors — not relevant to an HTML website
• Pandoc bumped to 3.6.3 — no API changes affecting `.qmd` website files

1.8 — Minor changes, all beneficial

• `posit-cloud` publish destination removed — chatlas publishes to `gh-pages`, unaffected
• Bootstrap Icons updated v1.11.1 → v1.13.1 — chatlas doesn't reference bootstrap icons directly in its config or SCSS
• IPython 9+ and plotly.py 6+ support — the chatlas docs site renders `.qmd` files only (no executed Jupyter notebooks in CI), so this is a non-issue
• Tabset a11y improvements — the site uses tabsets (`panel-tabset panel-pills`) and will benefit from the keyboard navigation fix
• `.quarto_ipynb` now auto-added to `.gitignore` in new projects — explains why this addition is canonical; the explicit addition in this PR is consistent

1.9 — Features enabled, no breakage

• `llms-txt: true` — this is the new feature being enabled; generates `llms.txt` index + per-page `.llms.md` markdown files
• `highlight-style` deprecated in favor of `syntax-highlighting` — chatlas doesn't use `highlight-style` in its config, so no impact; the old key remains supported anyway
• Navbar active state detection fix (#13506) — directly benefits the chatlas site's navbar/sidebar setup
• `SCSSParsingError` fix for non-ASCII SCSS selectors — `styles.scss` doesn't use non-ASCII selectors, but a defensive improvement regardless
• RevealJS scroll-view template change — not applicable (HTML website format only)

Conclusion

The upgrade from 1.6.26 to 1.9.37 is low-risk for this site. All breaking changes in the 1.7–1.9 range are scoped to LaTeX/PDF formats, RevealJS, or publish targets not used by chatlas. The site should build cleanly; the primary observable change is the new `llms.txt` artifact generated alongside the site.

Visual regression testing

Ran `tests/compare-sites/` against 189 pages (Quarto 1.6.26 build vs Quarto 1.9.37 build) using Playwright + Claude vision via AWS Bedrock. 0 regressions found.

Test plan

• Visual regression: 189/189 pages compared, 0 regressions (Quarto 1.6.26 → 1.9.37)
• Verify CI docs build passes with Quarto 1.9.37
• Confirm `llms.txt` is generated at the site root after build
• Check sidebar renders correctly with the new entries

[cpsievert]

@elnelson575 thanks for this, what else were you planning on here? Any chance we could push it over the finish line?

[elnelson575]

@elnelson575 thanks for this, what else were you planning on here? Any chance we could push it over the finish line?

Yep, I think I was just going to double-check that nothing in the site shifted and forgot to finish it off. I'll take a look now so we can get this out. 👍🏻