sync-repo-docs.mjs hardcodes standards_referenced: [] for every pulled product page

[jeremi]

Part of the 1.0 release-readiness push (see release/READINESS.md, section 3; blocks a trustworthy #199 inventory).

Context

docs/site/scripts/sync-repo-docs.mjs:270 writes standards_referenced: [] for every generated products/* page. Those pages are precisely where standards are described in the most detail (SD-JWT VC conformance profile, OID4VCI wallet interop, FHIR source adapter guide, and ~50 others), so the site's densest standards content is invisible to any tooling that keys off frontmatter, and check-doc-frontmatter.mjs has nothing to validate there. Only hand-authored explanation/* and spec/* pages carry real values.

Scope

• Populate standards_referenced for pulled pages: either read it from source-doc frontmatter in the product repos' docs, or from a per-page mapping in repo-docs.yaml.
• Validate the ids against src/data/standards.yaml like hand-authored pages.

Acceptance

• Pulled product pages carry accurate standards_referenced; frontmatter check covers them; regeneration is reproducible.

Security note

If this work surfaces a suspected vulnerability, report it per SECURITY.md; do not post details on this issue.