Add access review source freshness gates

[alejandrorivas-pixel]

Summary

• Add Source Freshness and Reconciliation evidence gates to access-review for HRIS, IdP, SaaS/native app, cloud IAM, and IGA campaign snapshots.
• Add AR-SRC-01 through AR-SRC-08 findings for stale exports, failed SCIM syncs, local-only accounts, post-snapshot privilege grants, missing replay evidence, and source-owner gaps.
• Add benign and vulnerable fixtures demonstrating fresh/replayable population evidence versus stale unreconciled review sources.

Validation

• git diff --check
• git diff --cached --check
• Markdown fence-balance check
• AR-SRC marker checks
• Benign/vulnerable fixture marker checks
• ASCII check for new fixture files
• Added-line sensitive-pattern scan

Closes #1561

Bounty target: structured review issue plus Improver Moderate if accepted. Payment details can be provided privately after maintainer acceptance.