feat: 新增 RealnamePolicy 常量枚举及 CodeRealnameNotAvailable 错误码

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

pkg/constants/iot.go

@@ -122,6 +122,13 @@ const (
 	AssetTypeDevice  = "device"   // 设备
 )
 
+// 实名认证策略
+const (
+	RealnamePolicyNone        = "none"         // 无需实名
+	RealnamePolicyBeforeOrder = "before_order" // 先实名后充值/购买
+	RealnamePolicyAfterOrder  = "after_order"  // 先充值/购买后实名
+)
+
 // 放款类型
 const (
 	PaymentTypeManual = "manual" // 人工打款