错误处理

{
  "code": 400,
  "message": "Bad Request",
  "error": {
    "field": "productId",
    "reason": "Product ID is required"
  }
}

{
  "code": 400,
  "message": "Bad Request",
  "error": {
    "field": "price",
    "reason": "Price must be at least 0.01"
  }
}

{
  "code": 401,
  "message": "Unauthorized"
}

{
  "code": 404,
  "message": "Not Found"
}

{
  "code": 429,
  "message": "Too Many Requests"
}

{
  "code": 0,
  "message": "success",
  "data": {
    // 响应数据
  }
}

{
  "code": 0,
  "message": "success",
  "data": {
    "items": [...],
    "pagination": {
      "page": 1,
      "size": 20,
      "total": 42,
      "totalPages": 3
    }
  }
}