docs(governance): show human review in content calibration

[bokelley]

Summary

• add explicit buyer-side and seller-side human reviewers to the calibration sequence
• show each review path as independently optional
• label human review as an internal process, not a new AdCP task

This is a documentation clarification only; it does not change protocol semantics.

Validation

• npm run test:docs-nav
• npm run test:owned-links
• npm run lint:schema-links
• git diff --check

[aao-secretariat]

Ladon verdict: Approve

Approve — documentation-only change to a Mermaid sequence diagram.

What I checked:

• Single file changed: docs/governance/content-standards/index.mdx (+11/-1). Under docs/governance/, not the published protocol surface (static/schemas/source/**, task definitions, docs/reference/**), so no changeset is required.
• No schema, task definition, or wire-shape change — schema↔docs coherence not implicated.
• Mermaid diagram parses cleanly: participants declared, opt blocks balanced; new buyer/seller human-reviewer branches are correctly labeled as internal review steps, not AdCP tasks.
• No oneOf/discriminator, released-artifact, or 3.1.x patch-eligibility concerns.

Gate checks:

• No no-auto-approve team match.
• gated_paths: false — row 2 does not fire (REVIEW_REQUIRED status is irrelevant when no gated path is touched).
• high_risk: false, no deletions/modifications of sensitive files.
• No findings of any severity.

No blocking or medium findings; rows 1–8 do not fire. Falls through to row 9.