curl --request POST \
  --url https://app.magna.so/api/external/v1/portals/creatives/upload-url \
  --header 'Content-Type: application/json' \
  --header 'x-magna-api-token: <api-key>' \
  --data '
{
  "fileName": "<string>",
  "contentType": "<string>"
}
'

{
  "isProcessed": true,
  "result": {
    "uploadUrl": "https://...signed-upload-url...",
    "storageKey": "images/portal/hero-abc123.png",
    "publicUrl": "https://.../images/portal/hero-abc123.png"
  }
}