Log CLI scan events to audit.log and add append test

[Jeffrin-dev]

Motivation

• Add an auditable record for CLI-initiated scans so scan outcomes are persisted for reporting and review.
• Ensure the CLI logging is append-safe by validating that consecutive runs create multiple JSON Lines entries in audit.log.

Description

• Updated shadowaudit/cli.py to import AuditLogger, AuditEvent, and datetime.timezone, and to use a scan_result variable after PIIScanner and SecretsDetector run.
• Constructed an AuditEvent with timestamp=datetime.now(timezone.utc).isoformat(), request_id=scan_result.request_id, scan_result=scan_result, policy_applied="none", model_target="cli", and response_clean=True, then appended it with AuditLogger("audit.log").append(...).
• Added test_scan_command_writes_and_appends_audit_log in tests/test_cli_scan.py which runs the scan command twice in a temporary directory and asserts audit.log exists and contains two JSONL lines.

Testing

• Ran pytest -q tests/test_cli_scan.py and the test file passed with 3 passed.

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Codex Task