fix(UserFirmMapper): 删除多余的amountOwed字段映射

- 移除UserFirmMapper.xml中c.amount_owed的映射
- 保持其余字段映射不变
- 优化查询字段，减少无用数据加载

src/main/resources/mapper/business/UserFirmMapper.xml

@@ -12,7 +12,6 @@
         b.name AS firmName,
         a.type,
         c.balance,
-        c.amount_owed AS amountOwed,
         IFNULL(d.total_consumption, 0) AS totalConsumption,
         a.create_time,
         a.create_by,