Complete multipart upload

Complete a multipart upload for an asset file. This endpoint finalizes the multipart upload by combining all uploaded parts, registers the original file on the asset (`assetId` is required) and triggers asset completion and media post-processing. **Two-step workflow:** 1. Upload the file parts to the signed URLs returned when the asset was created 2. Call this endpoint with `assetId` to complete the upload and trigger processing Post-processing failures after the upload has been committed do not fail the request — they are reported via the optional `warning` field.

curl -X POST "https://example.com/assets/complete-upload" \  -H "Content-Type: application/json" \  -d '{    "key": "string",    "uploadId": "string",    "assetId": "9179b887-04ef-4ce5-ab3a-b5bbd39ea3c8"  }'

{  "status": "completed",  "warning": "Post-processing failed"}