List partner customers

{
  "success": true,
  "customers": [
    {
      "customerId": "550e8400-e29b-41d4-a716-446655440000",
      "status": "active"
    },
    {
      "customerId": "660e8400-e29b-41d4-a716-446655440001",
      "status": "inactive"
    }
  ],
  "pagination": {
    "totalCount": 42,
    "page": 1,
    "pageSize": 20,
    "hasNextPage": true
  }
}

{
  "success": false,
  "error": "Failed to verify org API key"
}

{
  "success": false,
  "error": "Partner ID and API key are required in headers"
}

{
  "success": false,
  "error": "Failed to list partner customers"
}