Add agent discovery metadata for docs

[dimitri-circle]

Summary

• add truthful Auth.md, agent instructions, and a read-only documentation research skill
• add a narrowly routed Cloudflare Worker for RFC 8288 Link headers, RFC 9727 API catalog, MCP server card, Agent Skills index, and ARD manifest
• document the DNSSEC-validated DNS-AID SVCB record and rollback boundaries
• add the two human-readable agent pages to GitBook navigation

OAuth, A2A, WebMCP, registration, and payment metadata remain absent because this public documentation service does not provide those capabilities.

Verification

• node test suite: 9 of 9 passed
• Cloudflare versioned Preview URL: public scanner Level 4, Agent-Integrated
• production scanner after rollout: Level 4, with Link headers, DNS-AID, API catalog, MCP card, Agent Skills, and ARD passing
• production homepage SHA-256 remained unchanged across the edge rollout
• HTML and Markdown negotiation remained available
• representative documentation routes and robots.txt remained available
• live GitBook MCP initialize still returns protocol 2025-06-18 and the verified tool capability
• published skill SHA-256 matches the served bytes
• Cloudflare and Google DNS resolvers return AD=true for the DNS-AID record

Rollback

Remove only the four Worker routes declared in wrangler.jsonc and delete only the SVCB record declared in dns-aid-record.json. The GitBook CNAME is unchanged.