[daveh-beep]

docs: acknowledge related systems and standards

Problem

The documentation explains GAP's records and lifecycle but does not collect related work. Readers lack a single place to find adjacent content-generation systems, provenance models, and attestation standards, or understand how their scope relates to GAP.

Changes

• Add a Related work page under Intro with ten entries: SAGE, in-toto, SLSA, W3C Verifiable Credentials, C2PA, Nanopublications, RO-Crate, W3C PROV, SCITT, and DSSE.
• Cite primary sources and describe each work's contribution, shared concerns, and differences in scope. Pin GitHub specification references to reviewed commits and use versioned standards where available.
• Link the page from the Intro sidebar, Intro index, and repository README.
• Update route and navigation tests while preserving the existing four-section documentation hierarchy.

The page acknowledges related work without claiming endorsement, interoperability, priority, or direct influence on GAP's design. Possible integrations are distinguished from implemented behavior. Community documentation that remains unversioned is identified as such where applicable.

This is a documentation-only change. It adds no protocol requirements and changes no schemas, digest domains, examples, or demo behavior.

Verification

The following passed on the final commit, 6686234:

• pnpm docs:test
• pnpm --dir documentation typecheck
• pnpm docs:build
• DOCS_BASE_URL=/governed-artifact-protocol/ pnpm docs:build

The subpath build was reviewed locally at desktop and mobile sizes, with screenshots captured in both themes. Checked direct entry, sidebar placement, table of contents, ten entry headings, previous/next navigation, and mobile horizontal overflow.

All 21 original citation links returned HTTP 200 during research. The five GitHub references were subsequently pinned to reviewed commits, and all five pinned source documents were fetched successfully. All documentation checks passed again after pinning those references. The working tree is clean.