List service accounts

{
  "service_accounts": [
    {
      "id": "018f1a2b-0001-7000-8000-000000000050",
      "name": "Payment Processor Bot",
      "description": "Service account for payment gateway integration",
      "active": true,
      "created_at": "2026-01-15T08:00:00Z"
    }
  ],
  "total": 0,
  "page": 0,
  "limit": 0,
  "total_pages": 0
}

{
  "error": "unauthenticated",
  "message": "missing or invalid bearer token",
  "request_id": "req_01abc123"
}