🖼️ 圆形头像转换

POST http://www.98qy.com/picture/index.php?api=1
# 表单参数 (multipart/form-data)
image: photo.jpg          // 图片文件 (必填)
background: transparent    // white 或 transparent (可选，默认 white)

curl -X POST "http://www.98qy.com/picture/index.php?api=1" \
  -F "image=@/path/to/photo.jpg" \
  -F "background=transparent"

{
  "code": 200,
  "message": "success",
  "data": {
    "avatar": "iVBORw0KGgoAAAANSUhEUgAA...",
    "filename": "avatar_6a7ecf9390d5a.png",
    "url": "/picture/uploads/avatar_6a7ecf9390d5a.png",
    "background": "transparent",
    "size": 200,
    "expire_hours": 24
  }
}