refactor platform logic and add gasorder domain

backend/api/internal/models/gasorder_contract.go

@@ -0,0 +1,26 @@
+package models
+
+import (
+	"time"
+
+	"git.apinb.com/bsm-sdk/core/database"
+)
+
+// GasorderContract 对应 gasorder_contract，保存用户与气站唯一供气合同。
+type GasorderContract struct {
+	Entity                        // 公共实体字段
+	ContractNo         string     `gorm:"column:contract_no;type:varchar(64);not null;uniqueIndex" json:"contract_no"`                                // 合同编号
+	UserAccountID      uint64     `gorm:"column:user_account_id;not null;uniqueIndex:idx_gasorder_contract_party" json:"user_account_id"`             // 签约用户自增主键
+	GasBasicID         uint64     `gorm:"column:gas_basic_id;not null;uniqueIndex:idx_gasorder_contract_party" json:"gas_basic_id"`                   // 签约气站自增主键
+	DeliveryBasicID    uint64     `gorm:"column:delivery_basic_id;not null;default:0;index" json:"delivery_basic_id"`                                 // 默认配送点自增主键
+	Title              string     `gorm:"column:title;type:varchar(255);not null" json:"title"`                                                       // 合同标题
+	Terms              string     `gorm:"column:terms;type:text;not null;default:''" json:"terms"`                                                    // 合同条款
+	FileURI            string     `gorm:"column:file_uri;type:varchar(512);not null;default:''" json:"file_uri"`                                      // 合同文件地址
+	DefaultDeliveryFee int64      `gorm:"column:default_delivery_fee;not null;default:0;check:default_delivery_fee >= 0" json:"default_delivery_fee"` // 默认配送费，单位分
+	SignedAt           time.Time  `gorm:"column:signed_at;type:timestamptz;not null" json:"signed_at"`                                                // 签订时间
+	EffectiveAt        time.Time  `gorm:"column:effective_at;type:timestamptz;not null" json:"effective_at"`                                          // 生效时间
+	ExpiredAt          *time.Time `gorm:"column:expired_at;type:timestamptz" json:"expired_at"`                                                       // 到期时间
+}
+
+func init()                                       { database.AppendMigrate(&GasorderContract{}) }
+func (table *GasorderContract) TableName() string { return "gasorder_contract" }