feat(system):库区管理新增库区面积合计查询接口

新增 GET /storageSectionApi/sumStorageRegion，与库区列表 /list 相同筛选条件及组织数据权限，
SQL 端 IFNULL(SUM(storage_region),0) 返回面积合计(平方米)，无数据返回0；
抽取 queryList 数据权限为 applyQueryDataPermission 供列表与合计共用，/list 行为不变。

mhd-modules/mhd-system/src/main/resources/mapper/basic/storageSection/StorageSectionMapper.xml

@@ -102,4 +102,12 @@ PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
         <include refid="selectStorageSectionPo1"/>
         order by a.storage_name asc, a.create_time desc
     </select>
+
+    <!-- 库区面积合计：与 queryList 相同筛选条件，SUM(库区面积)，无数据时返回 0 -->
+    <select id="sumStorageRegion" parameterType="com.mhd.basic.domain.storageSection.repository.todo.StorageSectionDO" resultType="java.math.BigDecimal">
+        select IFNULL(SUM(a.storage_region), 0)
+        from storage_section a
+        LEFT JOIN warehouse w ON a.warehouse_id = w.warehouse_id AND w.del_flag = 1
+        <include refid="selectStorageSectionPo1"/>
+    </select>
 </mapper>