docs(readme): convert README.adoc -> Markdown README.md (#23)

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

@@ -0,0 +1,71 @@
+<!--
+SPDX-License-Identifier: CC-BY-SA-4.0
+SPDX-FileCopyrightText: 2025-2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+-->
+
+# Overview
+
+**Pre-commit hook for validating K9 configuration files.**
+
+K9 is a Nickel-based configuration contract format used for deployment
+validation and policy enforcement. This hook validates `.k9` and
+`.k9.ncl` files on commit.
+
+# Checks Performed
+
+1.  **K9! magic number** — First non-empty line must be exactly `K9!`
+
+2.  **SPDX header** — `SPDX-License-Identifier` in the first 10 lines
+
+3.  **Pedigree block** — `pedigree` `=` `{` `…` `}` with `name` and
+    `version` fields
+
+4.  **Security level** — `leash`/`security_level` must be `kennel`,
+    `yard`, or `hunt`
+
+5.  **Hunt-level signature** — Hunt files must include `signature` or
+    `signature_required`
+
+# Installation
+
+Add to your `.pre-commit-config.yaml`:
+
+```yaml
+repos:
+  - repo: https://github.com/hyperpolymath/k9-pre-commit
+    rev: v1.0.0
+    hooks:
+      - id: validate-k9
+```
+
+Then install:
+
+```bash
+pre-commit install
+```
+
+# Manual Usage
+
+You can also run the hook script directly:
+
+```bash
+./hooks/validate-k9.sh path/to/file.k9.ncl [more-files.k9 ...]
+```
+
+# Security Levels
+
+| Level    | Trust       | Requirements              |
+|----------|-------------|---------------------------|
+| `kennel` | Data-only   | No signature required     |
+| `yard`   | Validated   | Nickel contracts enforced |
+| `hunt`   | Full access | Signature required        |
+
+# Author
+
+Jonathan D.A. Jewell \<[j.d.a.jewell@open.ac](j.d.a.jewell@open.ac).uk\>
+
+# License
+
+SPDX-License-Identifier: CC-BY-SA-4.0
+
+See [LICENSE](LICENSE) for details.