[Bug] Validate core docs from modules changes #339

Why

A modules-only manifest, registry, command, or bundle-docs change can make core handoff and command documentation stale. Core now validates its docs against a checked-out modules source, but modules CI does not reciprocally validate the paired core catalogue.

What Changes

• Add a fail-closed modules-side wrapper that runs the core documentation-accountability checker against the paired core checkout and this modules checkout.
• Run it locally from pre-commit for module manifest, registry, bundle command, and documentation inputs.
• Run it as a blocking step in Docs Review after the workflow checks out the paired core ref.
• Include paired-worktree, unavailable-core, stale-core-catalogue, and manifest/root-change regression coverage.
• Keep the core checker authoritative; this change adds no duplicate package inventory.

Acceptance Criteria

• A modules-only change that adds/remaps/removes an official package or grouped root fails until paired core docs are updated.
• The modules docs workflow resolves the matching core branch when available and otherwise fails against the documented base fallback.
• The local gate fails closed with setup guidance when no paired core checkout is available.
• Core issue [Bug] Enforce official module documentation accountability specfact-cli#643 is recorded as the prerequisite because it supplies the authoritative checker.

OpenSpec Change Proposal: docs-16-core-accountability-sync