fix(audit): 修复充值审计列表排序字段

- 将 'free_gold' 字段名修改为 'freeGold'，以匹配后端接口实际字段名

src/views/audit/rechargeAudit.vue

@@ -581,7 +581,7 @@ const handleSortChange = (column) => {
   } else if (column.prop === 'permanentGold') {
     sortField.value = 'permanent_gold'
   } else if (column.prop === 'freeGold') {
-    sortField.value = 'free_gold'
+    sortField.value = 'freeGold'
   } else if (column.prop === 'createTime') {
     sortField.value = 'create_time'
   } else if (column.prop === 'payTime') {