Move the documentation from MkDocs to AsciiDoc, published on smallrye.io

[phillip-kruger]

The docs move from MkDocs to AsciiDoc, laid out like the Quarkus guides. smallrye.io pulls them in and publishes them at https://smallrye.io/docs/smallrye-mutiny-zero// (smallrye/smallrye.github.io#136): main nightly, each release once it is tagged.

Depends on smallrye/smallrye.github.io#136. The new Documentation check calls the reusable workflow added there.

What changes

• docs/*.md become docs/src/main/asciidoc/*.adoc with the same names, so the same addresses; the sidebar is _nav.yml, shared attributes are in _attributes.adoc, images stay under assets/.
• The Javadoc sidebar entry links to javadoc.io (the aggregated Javadoc was published together with the MkDocs site).
• Code examples stay in each module's src/test/java/docsamples (compiled and run by the build) and are included with include::{examples-dir}/...[].
• Pull requests touching docs/ or the samples run the new Documentation workflow: it renders the docs with the smallrye.io site, fails on a broken include or a page that does not render, and attaches the rendered site.
• Removed: mkdocs.yml, the theme override, pyproject.toml/uv.lock, the mike Publish the website workflow and .github/scripts/render-documentation.sh. Releases no longer publish docs; smallrye.io picks up the tag.
• docs/README.adoc explains how to write and preview pages; the README links to the new location.

Older versions

Everything already on gh-pages (1.3.1 and earlier) stays where it is, and the site's version picker links to it. After this is merged, the mike latest alias and the root page on gh-pages will redirect to /docs/smallrye-mutiny-zero/latest/.

Checked

Rendered with the smallrye.io site: no errors or Asciidoctor warnings, all internal links and images resolve.

[phillip-kruger]

Screenshots of the documentation before and after this change (updated).

Before: the MkDocs site, as it is on smallrye.io today. After: this branch's AsciiDoc, rendered by smallrye.io with smallrye/smallrye.github.io#136 (a local build: /docs/smallrye-mutiny-zero/main/). On smallrye.io the sidebar starts closed (the ☰ button opens it, and it stays open on the next pages for that reader); its groups are folded except the one holding the current page. The project and version picker sit in the header next to the logo, so a start page has no separate title; further down, a start page lists the documentation, from its navigation.

Before	After
Overview · old page
Quick start · old page
Quick start, with the Contents sidebar open