feat(content): publish AGENTS.md decision system article

[tcballard]

What changed

• publishes the canonical article AGENTS.md Is Not a Decision System;
• introduces the Record → Route → Enforce model for coding-agent decision governance;
• adds adjacent primary and research citations;
• adds page metadata and TechArticle JSON-LD;
• enables Markdown footnotes;
• adds the article to the knowledge-base navigation and homepage;
• relies on MkDocs to include the new canonical page in the generated sitemap.

Validation intent

The repository's pull-request workflow builds the knowledge base in strict mode. After checks pass, this PR should be squash-merged so the existing GitHub Pages workflow deploys the article.

Canonical URL

https://docs.asdecided.com/articles/agents-md-is-not-a-decision-system/