chore: exclude AGENTS.md and CLAUDE.md from markdownlint

Ref vergil-project/vergil-tooling#197

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: wphillipmoore

.markdownlintignore

@@ -1,3 +1,5 @@
 CHANGELOG.md
 releases/
 docs/announcements/
+AGENTS.md
+CLAUDE.md