统一响应格式

{
  "success": true,
  "task_id": "27a1128f-14b5-440e-a82d-510c81e6fcd4",
  "image_id": "1211290228438868029",
  "image_url": "https://midjourney.cdn.acedata.cloud/.../image.png",
  "image_width": 1024,
  "image_height": 1024,
  "actions": ["upscale1", "upscale2", "variation1", "variation2", ...]
}

{
  "error": {
    "code": "invalid_token",
    "message": "The specified token is invalid or wrong."
  },
  "trace_id": "2efa9340-b21b-4e26-9e14-4aac95f343ab"
}

{
  "success": true,
  "task_id": "...",
  "trace_id": "...",
  "image_url": "...",
  "...": "...（其余业务字段）"
}

{
  "success": false,
  "task_id": "...",
  "trace_id": "...",
  "error": {
    "code": "...",
    "message": "..."
  }
}