[Sync to prerelease] Replace prerelease-link-subdomain with version-aware shortcode

[github-actions]

Description

Sync of #1939 to prerelease.

Original PR

Replace prerelease-link-subdomain with version-aware shortcode

prerelease-link-subdomain is phase-aware but not version-aware. On the next RC cycle (e.g. v1.10), old blog posts about v1.9 features would incorrectly flip back to prerelease.quarto.org even though those docs already moved to quarto.org.

Fix

Replace the variable with a prerelease-docs-url shortcode extension that takes a version argument:

[PDF Accessibility](https://{{< prerelease-docs-url 1.9 >}}quarto.org/docs/output-formats/pdf-accessibility.html)

The shortcode uses two rules:

1. On the prerelease site (prerelease-docs profile active): always return prerelease.
2. On quarto.org: compare the arg to the version key in _quarto.yml using pandoc.types.Version. If arg <= version, docs are on quarto.org (return ""). If arg > version, docs are still only on prerelease (return prerelease.).

A new version key in _quarto.yml tracks the current stable release ('1.8' on main today). The _quarto-prerelease-docs.yml overrides it to '1.9' but the shortcode never reaches the comparison on the prerelease site (rule 1 short-circuits). The version drops the v prefix for clean comparison; the announcement banner adds it back inline.

Lifecycle of a blog post

A blog post on main announces a v1.9 feature using {{< prerelease-docs-url 1.9 >}}. The blog post itself never changes — the links flip automatically as releases happen:

On quarto.org (version comparison):

Phase	version in _quarto.yml	Arg	Comparison	Link
v1.9 in development	1.8	1.9	1.9 > 1.8	prerelease.quarto.org
v1.9 RC	1.8	1.9	1.9 > 1.8	prerelease.quarto.org
v1.9 released (version bumped)	1.9	1.9	1.9 <= 1.9	quarto.org
v1.10 in development	1.9	1.9	1.9 <= 1.9	quarto.org

On prerelease.quarto.org (prerelease-docs profile short-circuits):

All links always go to prerelease.quarto.org regardless of version, since the prerelease site hosts its own copy of the docs.

Testing

Verified each lifecycle row by rendering a test blog post and checking output links. For rows requiring a specific version value, _quarto.yml was temporarily edited.

Phase	Command	version	Result
v1.9 dev	quarto render <post>	1.8	prerelease.quarto.org
v1.9 RC	quarto render <post> --profile rc	1.8	prerelease.quarto.org
v1.9 released	quarto render <post>	1.9	quarto.org
v1.10 dev	quarto render <post> --profile prerelease	1.9	quarto.org
Prerelease site	quarto render <post> --profile "prerelease,prerelease-docs"	1.9	prerelease.quarto.org

Both quoted ("1.9") and unquoted (1.9) argument forms work correctly.

Follow-up to #1932, relates to #1934 and #1938.

[cderv]

/deploy-preview

[github-actions]

📝 Preview Deployment

🔍 Full site preview: https://deploy-preview-1943.quarto.org

🔄 Modified Documents

• docs/blog/posts/2026-03-05-pdf-accessibility-and-standards/index.qmd