fix: ListInstanceGroups 返回 enriched 数据含 instance IDs

- ListInstanceGroups 改用 enrichGroup 返回完整数据
- 包含 readonly_instance_ids/write_instance_ids 供前端穿梭框回显

backend/internal/handler/ghost.go

@@ -165,7 +165,11 @@ func ListWorkflows(c *gin.Context) {
 func ListInstanceGroups(c *gin.Context) {
 	var groups []model.InstanceGroup
 	model.DB.Order("id").Find(&groups)
-	c.JSON(http.StatusOK, groups)
+	result := make([]gin.H, len(groups))
+	for i, g := range groups {
+		result[i] = enrichGroup(g)
+	}
+	c.JSON(http.StatusOK, result)
 }
 
 // POST /api/v1/notifications/test