Move the documentation from Antora to AsciiDoc pages published on smallrye.io

[phillip-kruger]

The docs move from their own Antora site to AsciiDoc laid out like the Quarkus guides. smallrye.io pulls them in and publishes them at https://smallrye.io/docs/jandex// (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

• Pages. doc/modules/ROOT/pages/** become docs/src/main/asciidoc/** with the same paths, so the pages keep their names (core/indexing, maven/basic, …).
  • nav.adoc becomes _nav.yml; shared attributes are in _attributes.adoc.
  • Pages in subdirectories set :version-root: so shared paths work from any depth.
• PR check. Pull requests touching docs/ run the 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 as an artifact.
• Removed: the Antora component (doc/: antora.yml, playbooks), the Jandex GitHub Pages workflow, and the release job that ran it. The release no longer publishes docs; smallrye.io picks up the tag.
• Docs and README links. docs/README.adoc explains how to write and preview pages, and the README links to the new location.

Old addresses

The current site at https://smallrye.io/jandex/ (gh-pages, docs/jandex/main/*.html) stays where it is for now. Its pages will separately be replaced by redirects to the same page under https://smallrye.io/docs/jandex/latest/.

Checked

• The docs synced from this branch render with the smallrye.io site without errors or Asciidoctor warnings.
• All 205 internal links resolve, anchors included.

[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/jandex/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
Start page · old page
Indexing Classes · old page
Indexing Classes, with the Contents sidebar open

Dark theme: the same screenshots with the dark theme

The old Antora sites and the GraphQL, Vert.x bindings and Mutiny Zero MkDocs sites have no dark theme, so their "before" stays light; the other old MkDocs sites were switched to their own dark palette.

Before (dark theme)	After (dark theme)
Start page · old page
Indexing Classes · old page
Indexing Classes, with the Contents sidebar open

[Ladicek]

LGTM, but I'll wait with merging until smallrye/smallrye.github.io#136 is done, as advised there.