feat: 四个 Model 新增 realname_policy 字段（含 gorm 标签和中文注释）

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

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

internal/model/iot_card.go

@@ -54,6 +54,7 @@ type IotCard struct {
 	VirtualNo            string     `gorm:"column:virtual_no;type:varchar(50);uniqueIndex:idx_iot_card_virtual_no,where:deleted_at IS NULL AND virtual_no IS NOT NULL AND virtual_no <> '';comment:虚拟号(可选，非空时全局唯一)" json:"virtual_no,omitempty"`
 	DeviceVirtualNo      string     `gorm:"column:device_virtual_no;type:varchar(100);not null;default:'';comment:绑定设备的虚拟号快照(未绑定时为空字符串)" json:"device_virtual_no"`
 	LastGatewayReadingMB float64    `gorm:"column:last_gateway_reading_mb;type:float;not null;default:0;comment:上次轮询时网关返回的流量读数(MB)" json:"last_gateway_reading_mb"`
+	RealnamePolicy       string     `gorm:"column:realname_policy;type:varchar(20);default:'none';not null;comment:实名认证策略(none=无需实名,before_order=先实名后充值/购买,after_order=先充值/购买后实名)" json:"realname_policy"`
 }
 
 // TableName 指定表名