Closes five gaps where requirements could slip through unchecked at milestone
level: audit now cross-references VERIFICATION.md + SUMMARY frontmatter +
REQUIREMENTS.md traceability, integration checker receives req IDs, gap objects
carry plan-level detail, plan-milestone-gaps updates traceability, and
complete-milestone gates on requirements status.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>