移除摸大红支付后建群逻辑，仅保留扫码与复制

支付成功只固化客服二维码与订单文案；同步清理迁移、配置与前后端相关字段。

backend/internal/modules/mohong/order_repo.go

@@ -10,9 +10,7 @@ import (
 	"time"
 
 	"hfb_sys/backend/internal/model"
-	"hfb_sys/backend/internal/modules/chat"
 	"hfb_sys/backend/internal/modules/notification"
-	"hfb_sys/backend/internal/modules/supportgroup"
 	"hfb_sys/backend/internal/timeutil"
 	"hfb_sys/backend/pkg/money"
 
@@ -21,8 +19,6 @@ import (
 	"gorm.io/gorm/clause"
 )
 
-const ConversationTypeMohongOrder = "mohong_order"
-
 func (r *Repository) CreateOrder(ctx context.Context, userID uint64, req CreateOrderRequest) (*OrderDTO, error) {
 	if userID == 0 || req.ProductID == 0 || req.Quantity < 1 || req.Quantity > 99 {
 		return nil, ErrInvalidRequest
@@ -257,7 +253,8 @@ func (r *Repository) AdminCompleteOrder(ctx context.Context, orderID uint64, rem
 	return r.AdminFindOrder(ctx, orderID)
 }
 
-// ConfirmPaidFromChannelTx 支付成功后推进摸大红订单：建群、发固定码、写复制文案。
+// ConfirmPaidFromChannelTx 支付成功后推进摸大红订单：固化二维码快照与可复制文案。
+// 返回值固定为 0，兼容支付模块会话通知签名（摸大红无订单群）。
 func (r *Repository) ConfirmPaidFromChannelTx(tx *gorm.DB, orderID uint64) (uint64, error) {
 	var order model.MohongOrder
 	if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).First(&order, orderID).Error; err != nil {
@@ -265,9 +262,6 @@ func (r *Repository) ConfirmPaidFromChannelTx(tx *gorm.DB, orderID uint64) (uint
 	}
 	if order.Status == model.MohongOrderStatusPaid ||
 		order.Status == model.MohongOrderStatusCompleted {
-		if order.ConversationID != nil {
-			return *order.ConversationID, nil
-		}
 		return 0, nil
 	}
 	if order.Status != model.MohongOrderStatusPendingPayment {
@@ -283,34 +277,10 @@ func (r *Repository) ConfirmPaidFromChannelTx(tx *gorm.DB, orderID uint64) (uint
 	copyText := buildCopyText(r.loadCopyTemplate(tx), order, snap, user)
 	now := time.Now()
 
-	conv, err := ensureMohongOrderConversation(tx, order, user)
-	if err != nil {
-		return 0, err
-	}
-	welcome := r.loadWelcomeText(tx)
-	if err := chat.SendSystemMessageForTx(tx, conv.ID, welcome); err != nil {
-		return 0, err
-	}
-	if qrcodeURL != "" {
-		if err := chat.SendImageMessageForTx(tx, conv.ID, "👇 请扫码联系客服", qrcodeURL); err != nil {
-			return 0, err
-		}
-	} else {
-		if err := chat.SendSystemMessageForTx(tx, conv.ID, "固定二维码尚未配置，请将下方订单信息复制后联系客服。"); err != nil {
-			return 0, err
-		}
-	}
-	if copyText != "" {
-		if err := chat.SendSystemMessageForTx(tx, conv.ID, copyText+"\n\n（长按/复制后发送给客服）"); err != nil {
-			return 0, err
-		}
-	}
-
 	order.Status = model.MohongOrderStatusPaid
 	order.PaidAt = &now
 	order.QrcodeURLSnapshot = qrcodeURL
 	order.CopyText = copyText
-	order.ConversationID = &conv.ID
 	if err := tx.Save(&order).Error; err != nil {
 		return 0, err
 	}
@@ -320,20 +290,17 @@ func (r *Repository) ConfirmPaidFromChannelTx(tx *gorm.DB, orderID uint64) (uint
 		UserID:  order.UserID,
 		Type:    "order",
 		Title:   "摸大红订单支付成功",
-		Content: "支付已完成，请在群内查看二维码与订单信息。",
+		Content: "支付已完成，请在订单详情扫码联系客服，并复制订单信息发送。",
 		BizType: "mohong_order",
 		BizID:   &orderIDCopy,
 	}); err != nil {
 		return 0, err
 	}
-	return conv.ID, nil
+	return 0, nil
 }
 
-func (r *Repository) NotifyNewConversation(conversationID uint64) {
-	if conversationID > 0 && r.chatNotifier != nil {
-		r.chatNotifier.NotifyNewConversation(conversationID)
-	}
-}
+// NotifyNewConversation 兼容支付模块接口；摸大红不创建会话，空实现。
+func (r *Repository) NotifyNewConversation(conversationID uint64) {}
 
 func (r *Repository) cancelPendingOrderTx(tx *gorm.DB, order *model.MohongOrder, reason string) error {
 	// 归还预扣库存
@@ -367,65 +334,6 @@ func (r *Repository) orderDTO(ctx context.Context, row model.MohongOrder, includ
 	return &dto, nil
 }
 
-func ensureMohongOrderConversation(tx *gorm.DB, order model.MohongOrder, user model.User) (*model.ChatConversation, error) {
-	var existing model.ChatConversation
-	err := tx.Where("mohong_order_id = ?", order.ID).First(&existing).Error
-	if err == nil {
-		return &existing, nil
-	}
-	if err != gorm.ErrRecordNotFound {
-		return nil, err
-	}
-
-	now := time.Now()
-	title := "摸大红 " + order.OrderNo
-	if name := strings.TrimSpace(user.Nickname); name != "" {
-		title = "摸大红-" + name
-	}
-	conversation := model.ChatConversation{
-		MohongOrderID: &order.ID,
-		Type:          ConversationTypeMohongOrder,
-		Title:         title,
-		Status:        "active",
-	}
-	if err := tx.Create(&conversation).Error; err != nil {
-		return nil, err
-	}
-
-	participants := []model.ChatParticipant{
-		{
-			ConversationID:  conversation.ID,
-			ParticipantType: "user",
-			ParticipantID:   order.UserID,
-			Role:            "buyer",
-			JoinedAt:        now,
-			LastReadAt:      &now,
-		},
-	}
-	supportID, err := supportgroup.PickSupportAdmin(tx, supportgroup.GroupCodeRenterHandoff)
-	if err != nil {
-		return nil, err
-	}
-	if supportID <= 0 {
-		supportID = chat.DefaultSupportAdminID(tx)
-	}
-	if supportID > 0 {
-		participants = append(participants, model.ChatParticipant{
-			ConversationID:  conversation.ID,
-			ParticipantType: "admin",
-			ParticipantID:   supportID,
-			Role:            "support",
-			JoinedAt:        now,
-		})
-	}
-	for _, p := range participants {
-		if err := tx.Clauses(clause.OnConflict{DoNothing: true}).Create(&p).Error; err != nil {
-			return nil, err
-		}
-	}
-	return &conversation, nil
-}
-
 func buildCopyText(template string, order model.MohongOrder, snap productSnapshot, user model.User) string {
 	if strings.TrimSpace(template) == "" {
 		template = defaultOrderCopyTemplate