Add concurrency-safe run closure and validate stale-memory lifecycle

[anusbutt]

Summary

• add graphkeeper close run for atomic open-to-closed run transitions
• correct the shipped skill and command documentation for create, claim, and close
• preserve stale-claim supersession guidance and prior Benchmark B evidence
• add unit, integration, end-to-end, packaging, and 50-race performance coverage
• record a fresh two-session Benchmark B pass where both runs close successfully

Verification

• npm run typecheck
• npm run validator:check
• npm run test:unit
• npm run test:integration
• npm run test:e2e
• npm run test:security
• npm run test:performance
• npm test
• npm run package:smoke
• skill quick validation
• clean public-CLI quickstart

Benchmark note

Session 2 corrected and superseded the stale module location and closed its run. It also inspected more Git history than the minimal-freshness guidance recommends; the benchmark report preserves this as a follow-up observation.