feat: 客户关联产品并支持按产品圈选通知群体

新增客户-产品多对多关联，列表可按产品筛选并复制邮箱；发证/下单自动回填历史关联。

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/internal/service/order/order_service.go

@@ -3,6 +3,7 @@ package order
 import (
 	"backend/internal/dto"
 	"backend/internal/model"
+	customersvc "backend/internal/service/customer"
 	"backend/internal/service/payment"
 	"backend/utils"
 	"errors"
@@ -142,6 +143,7 @@ func (s *OrderService) CreateOrder(req dto.CreateOrderRequest, clientIP, userAge
 	if err := s.db.Create(&order).Error; err != nil {
 		return nil, errors.New("创建订单失败")
 	}
+	_ = customersvc.AttachProduct(s.db, customer.ID, product.ID)
 
 	// 6. 生成收银台地址 // Logan.Li
 	var checkoutURL string
@@ -365,6 +367,7 @@ func (s *OrderService) PaymentWebhook(req dto.PaymentWebhookRequest, clientIP st
 			if err := tx.Create(&lic).Error; err != nil {
 				return err
 			}
+			_ = customersvc.AttachProduct(tx, order.CustomerID, order.ProductID)
 			if err := tx.Model(&model.Order{}).Where("id = ?", order.ID).
 				Update("license_id", lic.ID).Error; err != nil {
 				return err
@@ -471,6 +474,7 @@ func (s *OrderService) ManualGrant(req dto.ManualGrantRequest, operatorID uint,
 	if err := s.db.Create(&lic).Error; err != nil {
 		return nil, errors.New("创建 License 失败")
 	}
+	_ = customersvc.AttachProduct(s.db, customer.ID, req.ProductID)
 
 	// 创建/更新权益记录 // Logan.Li
 	renewable := plan.PlanType != "perpetual" && plan.PlanType != "lifetime"