新功能(#76): 促销系统下单流程集成

- 新增促销规则/规格促销价/使用记录模型与幂等迁移
- EvaluatePromo 支持 new_user/inactive_user/campaign 规则判定
- purchase/preCreate 接入促销判定：命中促销时跳过百分比折扣
- activate 激活后按 order_no 幂等写入 promo_usage
- 订单模型和响应结构新增 promo_rule_id、promo_discount 字段

Co-authored-by: multica-agent <github@multica.ai>

internal/svc/serviceContext.go

@@ -21,6 +21,7 @@ import (
 	logmessage "github.com/perfect-panel/server/internal/model/logmessage"
 	"github.com/perfect-panel/server/internal/model/order"
 	"github.com/perfect-panel/server/internal/model/payment"
+	"github.com/perfect-panel/server/internal/model/promo"
 	"github.com/perfect-panel/server/internal/model/subscribe"
 	"github.com/perfect-panel/server/internal/model/system"
 	"github.com/perfect-panel/server/internal/model/ticket"
@@ -45,7 +46,7 @@ type ServiceContext struct {
 	ExchangeRate       float64
 	GeoIP              *IPLocation
 	SignatureValidator *signature.Validator
-	S3Store             *storage.S3Store
+	S3Store            *storage.S3Store
 
 	//NodeCache   *cache.NodeCacheClient
 	AuthModel       auth.Model
@@ -63,6 +64,7 @@ type ServiceContext struct {
 	RedemptionCodeModel      redemption.RedemptionCodeModel
 	RedemptionRecordModel    redemption.RedemptionRecordModel
 	PaymentModel             payment.Model
+	PromoModel               promo.Model
 	DocumentModel            document.Model
 	SubscribeModel           subscribe.Model
 	TrafficLogModel          traffic.Model
@@ -138,6 +140,7 @@ func NewServiceContext(c config.Config) *ServiceContext {
 		RedemptionCodeModel:   redemption.NewRedemptionCodeModel(db, rds),
 		RedemptionRecordModel: redemption.NewRedemptionRecordModel(db, rds),
 		PaymentModel:          payment.NewModel(db, rds),
+		PromoModel:            promo.NewModel(db, rds),
 		DocumentModel:         document.NewModel(db, rds),
 		SubscribeModel:        subscribe.NewModel(db, rds),
 		TrafficLogModel:       traffic.NewModel(db),