Creates a GCS resumable upload session behind our domain. The caller PUTs file chunks to the returned uploadUrl with Content-Range headers.
Clerk session JWT or Unkey API key passed as Bearer token
Original file name including extension
1Total file size in bytes. Must not exceed the format-specific limit (e.g. 30 MB for PDF/images, 2 GB for video/audio, 10 MB for documents)
MIME type (e.g. application/pdf, image/png)
1Upload initiated — use uploadUrl to PUT file chunks