feat: 绑定新邮箱时创建独立邮箱用户并转移订阅，而非挂在设备用户上

- bindEmailWithVerificationLogic: 新邮箱路径改为创建独立 email user + joinFamily
- familyBindingHelper: clearMemberSubscribes → transferMemberSubscribesToOwner，订阅转移给 owner 而非删除
- accountMergeHelper: 同步更新调用点

Co-Authored-By: claude-flow <ruv@ruv.net>

internal/logic/public/user/bindEmailWithVerificationLogic.go

@@ -87,24 +87,54 @@ func (l *BindEmailWithVerificationLogic) BindEmailWithVerification(req *types.Bi
 			return nil, errors.Wrapf(xerr.NewErrCode(xerr.DatabaseQueryError), "query email bind status failed")
 		}
 
-		authInfo := &user.AuthMethods{
-			UserId:         u.Id,
-			AuthType:       "email",
-			AuthIdentifier: req.Email,
-			Verified:       true,
+		// Create a new email user and establish family relationship
+		var emailUser *user.User
+		if txErr := l.svcCtx.DB.Transaction(func(tx *gorm.DB) error {
+			emailUser = &user.User{
+				Salt:              "default",
+				OnlyFirstPurchase: &l.svcCtx.Config.Invite.OnlyFirstPurchase,
+			}
+			if err := tx.Create(emailUser).Error; err != nil {
+				return errors.Wrapf(xerr.NewErrCode(xerr.DatabaseInsertError), "create email user failed: %v", err)
+			}
+			emailUser.ReferCode = uuidx.UserInviteCode(emailUser.Id)
+			if err := tx.Model(&user.User{}).Where("id = ?", emailUser.Id).Update("refer_code", emailUser.ReferCode).Error; err != nil {
+				return errors.Wrapf(xerr.NewErrCode(xerr.DatabaseUpdateError), "update refer code failed: %v", err)
+			}
+			authInfo := &user.AuthMethods{
+				UserId:         emailUser.Id,
+				AuthType:       "email",
+				AuthIdentifier: req.Email,
+				Verified:       true,
+			}
+			if err := tx.Create(authInfo).Error; err != nil {
+				return errors.Wrapf(xerr.NewErrCode(xerr.DatabaseInsertError), "create email auth method failed: %v", err)
+			}
+			return nil
+		}); txErr != nil {
+			return nil, txErr
 		}
-		if err = l.svcCtx.UserModel.InsertUserAuthMethods(l.ctx, authInfo); err != nil {
-			return nil, errors.Wrapf(xerr.NewErrCode(xerr.DatabaseInsertError), "bind email failed: %v", err)
+
+		// Join family: email user as owner, device user as member
+		if err = familyHelper.validateJoinFamily(emailUser.Id, u.Id); err != nil {
+			return nil, err
+		}
+		joinResult, err := familyHelper.joinFamily(emailUser.Id, u.Id, "bind_email_with_verification")
+		if err != nil {
+			return nil, err
 		}
 		token, err := l.refreshBindSessionToken(u.Id)
 		if err != nil {
 			return nil, err
 		}
 		return &types.BindEmailWithVerificationResponse{
-			Success: true,
-			Message: "email bound successfully",
-			Token:   token,
-			UserId:  u.Id,
+			Success:      true,
+			Message:      "email user created and joined family",
+			Token:        token,
+			UserId:       u.Id,
+			FamilyJoined: true,
+			FamilyId:     joinResult.FamilyId,
+			OwnerUserId:  joinResult.OwnerUserId,
 		}, nil
 	}