feat: add domain knowledge documentation to agent-ready plugin

[dgalarza]

Summary

• Adds a new docs/DOMAIN.md template to the agent-ready plugin that documents business domain concepts, terminology, and workflows
• Updates scaffold mode to seed DOMAIN.md by scanning model/entity names from the codebase
• Updates audit mode to check for DOMAIN.md existence and population
• References DOMAIN.md from the AGENTS.md template and docs structure

Motivation

Co-locating domain knowledge in the codebase proved more effective than external wikis (Notion, Confluence) because it's version-controlled, discoverable, and accessible to AI agents.

What changed

• New template (assets/domain-knowledge-template.md): Glossary, Core Workflows, Domain Relationships, and optional Regulatory/Compliance Context sections with opinionated template notes
• SKILL.md: New Step 5 in scaffold mode generates docs/DOMAIN.md by scanning model/entity/type names; audit mode checks DOMAIN.md coverage; summary highlights it as "the most valuable file for human and AI onboarding"
• claude-md-template.md: Added DOMAIN.md reference in Architecture section
• docs-structure-template.md: Added DOMAIN.md to directory layout and index

Test plan

• Run /agent-ready scaffold on a test repo and verify docs/DOMAIN.md is created with seeded terms
• Run /agent-ready audit on a repo without DOMAIN.md and verify it flags the gap
• Run /agent-ready audit on a repo with a stub DOMAIN.md and verify it identifies it as a stub
• Verify generated AGENTS.md references DOMAIN.md in the Architecture section