[Task] Add release guardrails, runbook updates, and rollback verification

[ashleyshaw]

Release Summary

Document the release guardrails needed to prove the tag is safe before it is cut and to explain how to recover if the run fails.

Milestones / Checklist

• Require explicit live-release confirmation or equivalent guardrail before mutation
• Make release-notes ref resolution strict in live mode
• Publish the release metadata needed for review and verification
• Update the release runbook and rollback instructions with the new safety gates

Acceptance Criteria

• The release process documents the pre-tag checks that must pass
• The release process documents how to abort a release safely
• The release process documents how to verify the tagged commit after publish
• Rollback instructions remain aligned with the release workflow

Additional Context

• Source pack: .github/projects/active/release-agent-hardening/
• Proposal spec: openspec-strict/children/01-4-task-release-guardrails-runbook-and-rollback.md

Definition of Ready (DoR)

• Documentation need is clear and well-defined
• Related docs/issues or files linked
• Acceptance criteria listed
• Estimate added if relevant
• Milestone/release assigned (if applicable)

Definition of Done (DoD)

• Documentation meets org standards and guidelines
• Changelog entry prepared for PR (CHANGELOG.md)
• Documentation reviewed for clarity and accessibility
• Screenshots/code examples included if relevant
• PR uses correct branch prefix (docs/)

[linear-code]

LS-925