feat(ci): add GitHub Actions workflow for markdown linting and valida…

[dspachos]

Summary

This PR delivers a comprehensive overhaul of the Drupal AI Agent Development Guides repository, including a major content refresh, a new hosting variant, an experimental knowledge-base architecture, CI tooling, and an install script.

Changes

🐳 Lagoon Variant (new)

• Lagoon/AGENTS.md — New comprehensive guide for amazee.io Lagoon (Kubernetes-based hosting) with Lagoon CLI, lagoon-sync, Drush aliases, auto-deployment, Varnish/Redis, and post-rollout tasks.

📝 Content Refresh

• DDEV/AGENTS.md (+1,259 / −214) — Rewritten and expanded with updated patterns, code examples, and modern Drupal 10/11 best practices.
• Vanilla/AGENTS.md (+1,260 / −238) — Same level of refresh for traditional server environments.

🧪 Experimental: Knowledge Base Architecture

• experimental/AGENTS.md — Slim 60-line entry point (~400 tokens) replacing the monolithic ~1,500-line file.
• experimental/.kb/ — 23 focused knowledge-base files (topics indexed 00–22) that agents read on demand, cutting token usage from ~8,000 to ~400 for simple tasks.
• experimental/install.sh — One-liner installer with variant selection (--variant=ddev|lagoon|vanilla), branch targeting, and --kb-only / --no-kb options.
• experimental/README.md — Full documentation on the architecture, token savings table, install instructions, and feedback process.

🔧 CI & Quality Tooling

• .github/workflows/validate.yml — GitHub Actions workflow for markdown linting and validation.
• .markdownlint.json / .markdownlintignore — Markdown linting config.
• .prettierrc / .prettierignore — Prettier formatting config.
• .gitignore — Expanded ignores.
• package.json — Node dependencies for lint/format tooling.

📚 Documentation

• README.md — Restructured with table of contents, variant comparison table, expanded sections, and a banner linking to the experimental architecture.
• CONTRIBUTING.md — New contributor guidelines.
• CHANGELOG.md — New changelog tracking project history.

Files Changed

Area	Files	Additions	Deletions
AGENTS.md guides (DDEV, Vanilla, Lagoon)	3	~3,944	~452
Experimental KB architecture	26	~2,287	0
CI / quality tooling	6	~103	0
Documentation (README, CONTRIBUTING, CHANGELOG)	3	~286	~34
Total	39	+6,888	−486

Testing

• Markdown linting passes via npm run lint
• experimental/install.sh tested with all variants (--variant=vanilla|ddev|lagoon)
• Knowledge-base cross-references and internal links verified
• AGENTS.md files reviewed for Drupal 10/11 compatibility

Screenshots / Demos

Token savings comparison (experimental KB architecture):

Scenario	Monolithic	Knowledge Base
Simple task (fix typo)	~8,000 tokens	~400 tokens
Build a form	~8,000 tokens	~400 + ~1,200
Complex task (3 topics)	~8,000 tokens	~400 + ~3,500