Add hub sync and report cohorts CLI commands with pytest coverage, document
sibling index publish contract and hub hardening path, align INTENT layout,
raise external evidence on three registry entries, and close gap priorities
19-23 (priority 18 deferred on sibling index blocks).
Align INTENT.md with delivered layout, add CapabilityRegistryConcept guide,
extend schema with promotion_history, ship reuse-surface validate/query/export
CLI, register three more helix_forge capabilities, and refresh SCOPE and gap
analysis to reflect A3 tooling and D5/A3/C4/R2 self-assessment.
