Fix cross-platform CI regressions

[KeyffMS]

Summary

Fixes the regressions observed in the latest PlanAnvil CI run without weakening the contract or safety gates.

Changes

• canonicalize event repository paths before active-run routing for macOS/Windows path aliases;
• make checkpoint recovery assertions use canonical paths;
• update the artifact-sealing lock regression test to observe validate_plan_contract;
• make the Git hook probe fixture emit explicit hook diagnostics while preserving fail-closed classification;
• synchronize golden blind-review fixtures with the required plan-anvil-reviewer author role;
• update dependent comparison sidecar hashes;
• document the fixes in CHANGELOG.md.

Validation target

This PR intentionally relies on the existing pull_request workflow to run the full Python 3.11 suite on Ubuntu, macOS, and Windows.