fix: add missing brand field to markdown frontmatter

Follow-up to merge 5463925 - the merge kept main's version of markdown
files which were missing the 'brand' field required by the template.
All 6 markdown files in a2ml/site and k9-svc/site now have the brand field.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

Author: hyperpolymath

a2ml/site/index.md

@@ -3,6 +3,7 @@
 ---
 title: A2ML
 site: A2ML
+brand: A2ML
 description: A2ML is a lightweight, Djot-like markup that compiles into a typed, attested core, with progressive strictness from lax to fully attested.
 date: 2026-06-29
 ---

a2ml/site/spec.md

@@ -3,6 +3,7 @@
 ---
 title: A2ML specification
 site: A2ML
+brand: A2ML
 description: The normative A2ML v1.1.0 specification — surface grammar, typed core, profiles, and conformance test vectors.
 date: 2026-06-29
 ---

a2ml/site/start.md

@@ -3,6 +3,7 @@
 ---
 title: Get started with A2ML
 site: A2ML
+brand: A2ML
 description: Write, validate and render A2ML in three steps — from a plain-text document to a portable, typed core.
 date: 2026-06-29
 ---

k9-svc/site/index.md

@@ -3,6 +3,7 @@
 ---
 title: K9-SVC
 site: K9-SVC
+brand: K9-SVC
 description: K9-SVC is a Nickel-based format for self-validating configuration and contractiles, with a three-level trust model from inert data to signed execution.
 date: 2026-06-29
 ---

k9-svc/site/spec.md

@@ -3,6 +3,7 @@
 ---
 title: K9-SVC specification
 site: K9-SVC
+brand: K9-SVC
 description: The normative K9-SVC v1.0.0-alpha specification — the three-level trust model, media type, and conformance fixtures.
 date: 2026-06-29
 ---

k9-svc/site/start.md

@@ -3,6 +3,7 @@
 ---
 title: Get started with K9-SVC
 site: K9-SVC
+brand: K9-SVC
 description: Write, contract and sign a K9-SVC component in three steps, across all three trust levels.
 date: 2026-06-29
 ---