Verify the APPROVE evidence control on the deployed reviewer (real-container check, sandboxMountRoots) #473

What is left after #462

#462 (merged as 561853f) makes APPROVE require host-recorded passing evidence. Two checks remain before the control can be relied on in the deployed reviewer:

• Run the real-container evidence check (per-job-isolation-checks.sh records evidence and checks the record) on a host with Docker, against a good record, a wrong commit and a wrong key.
• Configure sandboxMountRoots on the reviewer host to list every actual sandbox bind, and confirm an evidence store or key under any of them is refused (approval_evidence_reachable).

Until both are done, the plugin's evidence check is verified by unit and integration tests only.