feat: 新增店铺联级查询接口

- 新增 GET /api/admin/shops/cascade 接口，支持按店铺名模糊查询和上级ID过滤
- Store 层新增 ListForCascade（支持数据权限过滤）和 GetParentIDsWithChildren 方法
- Service 层新增 ListCascade，批量判断 has_children 避免 N+1 查询
- 返回格式：[{id, shop_name, has_children}]

💘 Generated with Crush

Assisted-by: Claude Sonnet 4.6 via Crush <crush@charm.land>

internal/routes/shop.go

@@ -43,6 +43,14 @@ func registerShopRoutes(router fiber.Router, handler *admin.ShopHandler, doc *op
 		Output:  nil,
 		Auth:    true,
 	})
+
+	Register(shops, doc, groupPath, "GET", "/cascade", handler.Cascade, RouteSpec{
+		Summary: "店铺联级查询",
+		Tags:    []string{"店铺管理"},
+		Input:   new(dto.ShopCascadeRequest),
+		Output:  new([]dto.ShopCascadeItem),
+		Auth:    true,
+	})
 }
 
 func registerShopRoleRoutes(router fiber.Router, handler *admin.ShopRoleHandler, doc *openapi.Generator, basePath string) {