Create a remix task from an existing video.

Create a remix task from an existing video. This endpoint is derived from the current new-api router code and returns a unified management API response; the specific `data` structure varies by business object.

curl -X POST "https://example.com/v1/videos/0/remix" \  -H "Content-Type: application/json" \  -d '{    "model": "veo-3.1-generate-preview",    "prompt": "string"  }'

{
  "success": true,
  "message": "string",
  "data": null
}