docs: record workspace db persistence merge

[yha9806]

Summary

• record yha9806/vulca-platform PR feat: add real brief workflow adapter #35 and merge commit 24efaab5101494cfa7777aa3ded6d8c27e923870
• update the Workspace persistence spec, source index, durable-review status, release-readiness gate, M5 closeout, and manifest
• preserve the boundary that PR feat: add real brief workflow adapter #35 is DB-backed compatibility snapshot persistence, not full production authorization/conflict/audit/typed-aggregate/multi-instance readiness

Verification

• python3 docs/review-context/gates/validate_review_context.py
• python3 -m pytest tests/test_review_context_vault.py -q
• git diff --check
• git diff --cached | gemini-agent diff-review --stdin