test: keep blocked audit export trail beside the log file

[FabioLeitao]

Summary

• Cover the feat(observability): self-scan de logs p/ PII cleartext antes de persistir/export (dogfood vaultless) #877 retarget in _audit_log_file_response: a blocked /logs export writes AuditTrailFinding next to the exported file, not in a directory the audit logger was already using.
• The finding line stays category counts. The synthetic cleartext value is not in the trail file or the HTTP body.

Risky behavior now covered

configure_audit_log_directory(path.parent) runs before log_audit_trail_finding. Without this test, a later edit can drop that call and the trail goes back to whatever directory the process logger already had (often the working directory), while /logs still returns 422.

Test files

• tests/test_log_self_scan.py — test_blocked_export_writes_audit_trail_beside_the_exported_file

Test plan

• uv run pytest tests/test_log_self_scan.py
• ./scripts/check-all.sh --enforced (exit 0)