docs(readme): convert README.adoc -> Markdown (renders on Glama/profile/community-health) (#39)

README was AsciiDoc → renders as raw markup in Markdown consumers (Glama
MCP directory, GitHub community-health, GitHub profile). pandoc
asciidoc→GFM (badges → clickable), SPDX header kept, duplicate `.adoc`
removed. Part of the estate README-format fix.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -1,26 +1,27 @@
-[![Sponsor](https://img.shields.io/badge/Sponsor-%E2%9D%A4-pink?logo=github)](https://github.com/sponsors/hyperpolymath)
+<!--
+SPDX-License-Identifier: CC-BY-SA-4.0
+SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+-->
 
-// SPDX-License-Identifier: CC-BY-SA-4.0
-// Copyright (c) 2026 Jonathan D.A. Jewell (hyperpolymath)
+Showcase examples and templates for A2ML (AI Attestation Markup
+Language).
 
-= a2ml-showcase
+[![OpenSSF Scorecard](https://api.securityscorecards.dev/projects/github.com/hyperpolymath/a2ml-showcase/badge)](https://securityscorecards.dev/viewer/?uri=github.com/hyperpolymath/a2ml-showcase)
 
-Showcase examples and templates for A2ML (AI Attestation Markup Language).
+# About
 
-image:https://api.securityscorecards.dev/projects/github.com/hyperpolymath/a2ml-showcase/badge[OpenSSF Scorecard,link=https://securityscorecards.dev/viewer/?uri=github.com/hyperpolymath/a2ml-showcase]
+This repository contains example A2ML documents, templates, and rendered
+output demonstrating the capabilities of the A2ML format. It is a
+content/showcase repository — there is no executable code.
 
-== About
+# Structure
 
-This repository contains example A2ML documents, templates, and rendered output
-demonstrating the capabilities of the A2ML format. It is a content/showcase
-repository -- there is no executable code.
+- `content/` — A2ML source documents
 
-== Structure
+- `output/` — Rendered output
 
-* `content/` -- A2ML source documents
-* `output/` -- Rendered output
-* `template.html` -- HTML rendering template
+- `template.html` — HTML rendering template
 
-== License
+# License
 
-MPL-2.0. See link:LICENSE[LICENSE].
+MPL-2.0. See [LICENSE](LICENSE).