Move validate-prd from a workflow entry in create-prd manifest to a
self-contained skill at src/bmm/workflows/2-plan-workflows/bmad-validate-prd/.
Update pm.agent.yaml and module-help.csv to use skill: URI.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Alex Verkhovsky