docs(readme): convert README.adoc -> Markdown README.md

README must be real Markdown to render in GitHub community-health, the GitHub
profile, and external MCP directories (Glama) — AsciiDoc shows as raw markup
there. pandoc asciidoc->GFM, badges fixed to clickable, SPDX header kept as an
HTML comment, duplicate README.adoc removed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath

README.adoc

@@ -1,32 +1,38 @@
-[![Sponsor](https://img.shields.io/badge/Sponsor-%E2%9D%A4-pink?logo=github)](https://github.com/sponsors/hyperpolymath)
-
-= a2ml-validate-action
-:toc: preamble
-:icons: font
+<!--
+SPDX-License-Identifier: CC-BY-SA-4.0
+SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+-->
 
-== Overview
+# Overview
 
 **GitHub Action to validate A2ML manifest files in your repository.**
 
-A2ML (Agnostic Agent Markup Language) is a manifest format used across RSR
-(Rhodium Standard Repository) projects to declare machine-readable metadata,
-AI agent instructions, and project state. This action scans for `.a2ml` files
-and validates their structure and required fields.
+A2ML (Agnostic Agent Markup Language) is a manifest format used across
+RSR (Rhodium Standard Repository) projects to declare machine-readable
+metadata, AI agent instructions, and project state. This action scans
+for `.a2ml` files and validates their structure and required fields.
+
+# Checks Performed
+
+1.  **SPDX header** — Verifies `SPDX-License-Identifier` is present in
+    the first 10 lines
+
+2.  **Identity fields** — Requires `agent-id`, `name`, or `project`
+    field (relaxed for AI-MANIFEST files)
+
+3.  **Version field** — Checks for `version` or `schema_version`
 
-== Checks Performed
+4.  **Attestation blocks** — If an `[attestation]` section exists,
+    validates it contains `proof`, `signature`, or `hash` fields
 
-1. **SPDX header** — Verifies `SPDX-License-Identifier` is present in the first 10 lines
-2. **Identity fields** — Requires `agent-id`, `name`, or `project` field (relaxed for AI-MANIFEST files)
-3. **Version field** — Checks for `version` or `schema_version`
-4. **Attestation blocks** — If an `[attestation]` section exists, validates it contains `proof`, `signature`, or `hash` fields
-5. **Section syntax** — Warns on malformed `[section]` headings with unclosed brackets
+5.  **Section syntax** — Warns on malformed `[section]` headings with
+    unclosed brackets
 
-== Usage
+# Usage
 
 Add to your workflow:
 
-[source,yaml]
-----
+```yaml
 name: Validate A2ML
 on: [push, pull_request]
 
@@ -44,70 +50,44 @@ jobs:
           strict: 'false'  # Promote warnings to errors (default: false)
           # paths-ignore: defaults to vendored / fixture patterns; override
           # via newline-separated string. Use '' to disable.
-----
-
-=== Inputs
-
-[cols="1,1,3"]
-|===
-| Input | Default | Description
-
-| `path`
-| `.`
-| Directory path to scan for `.a2ml` files
-
-| `strict`
-| `false`
-| When `true`, warnings become errors and the action fails on any issue
-
-| `paths-ignore`
-| _vendored & fixture defaults_
-| Newline-separated path fragments to skip. Substring match against each
-  file path. Default set: `vendor/`, `vendored/`, `verified-container-spec/`,
-  `.audittraining/`, `integration/fixtures/`, `test/fixtures/`,
-  `tests/fixtures/`. Pass an empty string (`paths-ignore: ''`) to disable
-  and scan everything. See https://github.com/hyperpolymath/hypatia/pull/243
-  for the architectural rationale (content-pattern validators must
-  distinguish targets from fixtures / vendored / training-corpus files
-  that legitimately contain the very pattern being checked).
-|===
-
-==== Why default-on path exemptions?
+```
 
-A2ML files inside vendored projects (e.g. `verified-container-spec/`) have
-their own identity declarations elsewhere or are themselves training corpora.
-Flagging every such file as "missing identity field" is provenance noise,
-not signal. The defaults match the canonical RSR vendored-content paths;
-override for project-specific carve-outs.
+## Inputs
 
-=== Outputs
+| Input | Default | Description |
+|----|----|----|
+| `path` | `.` | Directory path to scan for `.a2ml` files |
+| `strict` | `false` | When `true`, warnings become errors and the action fails on any issue |
+| `paths-ignore` | *vendored & fixture defaults* | Newline-separated path fragments to skip. Substring match against each file path. Default set: `vendor/`, `vendored/`, `verified-container-spec/`, `.audittraining/`, `integration/fixtures/`, `test/fixtures/`, `tests/fixtures/`. Pass an empty string (`paths-ignore:` `’’`) to disable and scan everything. See <https://github.com/hyperpolymath/hypatia/pull/243> for the architectural rationale (content-pattern validators must distinguish targets from fixtures / vendored / training-corpus files that legitimately contain the very pattern being checked). |
 
-[cols="1,3"]
-|===
-| Output | Description
+### Why default-on path exemptions?
 
-| `files-scanned`
-| Number of `.a2ml` files processed
+A2ML files inside vendored projects (e.g. `verified-container-spec/`)
+have their own identity declarations elsewhere or are themselves
+training corpora. Flagging every such file as "missing identity field"
+is provenance noise, not signal. The defaults match the canonical RSR
+vendored-content paths; override for project-specific carve-outs.
 
-| `errors`
-| Count of validation errors
+## Outputs
 
-| `warnings`
-| Count of validation warnings
-|===
+| Output          | Description                       |
+|-----------------|-----------------------------------|
+| `files-scanned` | Number of `.a2ml` files processed |
+| `errors`        | Count of validation errors        |
+| `warnings`      | Count of validation warnings      |
 
-== Strict Mode
+# Strict Mode
 
-In strict mode (`strict: 'true'`), all warnings are promoted to errors. This
-is useful for repositories that require full A2ML compliance, such as those
-following the RSR standard.
+In strict mode (`strict:` `’true’`), all warnings are promoted to
+errors. This is useful for repositories that require full A2ML
+compliance, such as those following the RSR standard.
 
-== Author
+# Author
 
-Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+Jonathan D.A. Jewell \<[j.d.a.jewell@open.ac](j.d.a.jewell@open.ac).uk\>
 
-== License
+# License
 
 SPDX-License-Identifier: CC-BY-SA-4.0
 
-See link:LICENSE[LICENSE] for details.
+See [LICENSE](LICENSE) for details.