Returns a zip_token for downloading a folder (one entry in dirents) or several items (multiple dirents) as ZIP.

Workflow: get the token, poll Query task progress (/api/v2.1/query-zip-progress/?token=...) until zipped equals total, then download https://<server>/seafhttp/zip/{zip_token}.

The GET variant is marked as deprecated in SecureCloud (long dirents lists can exceed the URL length); SecureCloud also accepts the same parameters as POST body.