GET /v2/custodian-auth-flows

List all available custodian auth flows.

Note: marked "not yet available" in the public docs. May 404 in
production.

Path params: none.
Query params: none.

Response (200 OK):
{
  "data": [
    {
      "id": "string — e.g. nordea-20260630",
      "type": "custodian-auth-flow",
      "attributes": {
        "expectedFiles": [
          {
            "name":        "string — e.g. power-of-attorney",
            "description": "string",
            "fileType":    "string — e.g. pdf"
          }
        ],
        "supportedConsentTypes": [ "all", "specific" ]
      },
      "relationships": {
        "custodian": { "data": { "type": "custodian", "id": "string" } }
      }
    }
  ]
}