docs(po): Story 8.4 final compliance closure and lifecycle completion

[bychrisr]

Summary

• add full FR/NFR coverage matrix mapping requirements to implementation and validation evidence
• add final compliance closure document with go/no-go rationale, open blockers and residual risks
• close story lifecycle by moving stories 1.1 through 8.3 from Review to Done
• update Story 8.4 to Review with completion notes and QA evidence

Artifacts

• docs/requirements-coverage-matrix.md
• docs/final-compliance-closure.md
• docs/stories/8.4.story.md
• docs/stories/*.story.md (status closure updates)

Validation

• compliance evidence references existing validated gates:
  • npm run ci:local
  • npm run release:readiness
  • npm run e2e:smoke:gate