GET /api/v1/attackers/{uuid}/export/stix returns a self-contained STIX
2.1 bundle: ip observation, threat-actor, ATT&CK attack-patterns with
canonical MITRE IDs, uses relationships, per-tag sightings, file SCOs
for artifacts, domain-name SCOs for SMTP targets, and a provider intel
note. Attack-pattern SDOs carry the MITRE bundle IDs so consumers
deduplicating against the public ATT&CK bundle get exact matches.
