curl --request GET \
  --url https://api.example.com/api/audit-trail/stats \
  --header 'Authorization: Bearer <token>'

{
  "by_event_type": {},
  "by_category": {},
  "by_severity": {},
  "by_actor": {},
  "total": 0,
  "usage_by_day": [
    {
      "date": "<string>",
      "total_records": 0
    }
  ]
}