Train12306PayFormData

当前 handler 返回内部供应商结构，JSON 字段名保持 Go 导出字段的 PascalCase。

{
    "OrderID": "TO202607150001",
    "VendorOrderID": "E123456789",
    "State": true,
    "FailMsg": "",
    "Form": 1,
    "PayURL": "https://pay.12306.cn/example"
}