Link agent_docs Instead of Pasting API Docs

Never paste full API documentation into CLAUDE.md or AGENTS.md. Instead, link to documentation files in dedicated directories like docs/ or agent_docs/ so the agent reads them only when relevant.

## Supplementary Documentation
- For internal payment gateway webhook schemas, read ./agent_docs/payments-api.md.
- For multi-tenant row-level security policies, read ./agent_docs/rls-architecture.md.