feat: 新增店铺时自动设置默认角色

- CreateShopRequest 新增必填字段 default_role_id
- 创建店铺时验证默认角色（必须存在、是客户角色、已启用）
- 创建店铺后自动设置 ShopRole，初始账号立即拥有权限

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/service/shop/service.go

@@ -68,6 +68,18 @@ func (s *Service) Create(ctx context.Context, req *dto.CreateShopRequest) (*dto.
 		return nil, errors.New(errors.CodePhoneExists, "初始账号手机号已存在")
 	}
 
+	// 验证默认角色：必须存在、是客户角色且已启用
+	defaultRole, err := s.roleStore.GetByID(ctx, req.DefaultRoleID)
+	if err != nil {
+		return nil, errors.New(errors.CodeNotFound, "默认角色不存在")
+	}
+	if defaultRole.RoleType != constants.RoleTypeCustomer {
+		return nil, errors.New(errors.CodeInvalidParam, "店铺默认角色必须是客户角色")
+	}
+	if defaultRole.Status != constants.StatusEnabled {
+		return nil, errors.New(errors.CodeInvalidParam, "默认角色已禁用")
+	}
+
 	shop := &model.Shop{
 		ShopName:     req.ShopName,
 		ShopCode:     req.ShopCode,
@@ -108,6 +120,18 @@ func (s *Service) Create(ctx context.Context, req *dto.CreateShopRequest) (*dto.
 		return nil, errors.Wrap(errors.CodeInternalError, err, "创建初始账号失败")
 	}
 
+	// 设置店铺默认角色
+	shopRole := &model.ShopRole{
+		ShopID:  shop.ID,
+		RoleID:  req.DefaultRoleID,
+		Status:  constants.StatusEnabled,
+		Creator: currentUserID,
+		Updater: currentUserID,
+	}
+	if err := s.shopRoleStore.BatchCreate(ctx, []*model.ShopRole{shopRole}); err != nil {
+		return nil, errors.Wrap(errors.CodeInternalError, err, "设置店铺默认角色失败")
+	}
+
 	return &dto.ShopResponse{
 		ID:           shop.ID,
 		ShopName:     shop.ShopName,