Get presigned upload URL

curl -X POST https://app.mavera.io/api/v1/files/upload-url \
  -H "Authorization: Bearer mvra_live_your_key_here" \
  -H "Content-Type: application/json" \
  -d '{
    "file_name": "image.png",
    "file_type": "image/png",
    "file_size": 524288,
    "workspace_id": "ws_abc123"
  }'

{
  "object": "upload_url",
  "upload_url": "<string>",
  "public_url": "<string>",
  "key": "<string>",
  "expires_in": 123,
  "method": "PUT",
  "headers": {
    "Content-Type": "<string>",
    "x-amz-checksum-sha256": "<string>"
  },
  "next_step": {
    "description": "<string>",
    "endpoint": "<string>",
    "body": {}
  }
}