fix(AUD-009): audit log estructurado con exportación SIEM

[Axlfc]

Implements structured SIEM-exportable audit logging for Cognito (AUD-009):

1. Defined AuditLogRecord schema with actor (user_id/org_id), action, resource, timestamp, trace_id, and result.
2. Captured events via AUD-020 lifecycle hooks (on_agent_start, on_tool_pre_exec, on_tool_post_exec).
3. Persisted records in shared DB table (DBStructuredAuditLog) using append-only semantics.
4. Exported structured audit events via Syslog RFC 5424 (socket) and HTTP POST Webhooks (urllib).
5. Migrated ApprovalDecisionAudit (AUD-021) to the unified audit log as single source of truth.
6. Updated AUDIT_MASTER.md marking AUD-009 as Corregido.
7. Added unit test suite in tests/test_audit_log_siem.py.

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PR created automatically by Jules for task 4428201845066001580 started by @Axlfc

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