fix: 默认订单状态筛选改为全部(null)，重置时同步清空状态筛选

- form.status 初始值从 0(待处理) 改为 null(全部)
- handleReset 中 status 重置也改为 null
- 解决进入页面默认只显示待处理订单、其他状态订单不可见的问题

web/src/views/OrderManagement.vue

@@ -127,7 +127,7 @@ const props = defineProps({
 })
 defineEmits(['query', 'exportExcel', 'openImport'])
 
-const form = reactive({ receiver_name: '', receiver_phone: '', order_no: '', status: 0 })
+const form = reactive({ receiver_name: '', receiver_phone: '', order_no: '', status: null })
 const dateRange = ref(null)
 const currentPage = ref(1)
 const pageSize = ref(20)
@@ -150,7 +150,7 @@ function getParams() {
 }
 
 function handleReset() {
-  form.receiver_name = ''; form.receiver_phone = ''; form.order_no = ''; form.status = 0
+  form.receiver_name = ''; form.receiver_phone = ''; form.order_no = ''; form.status = null
   dateRange.value = null
   currentPage.value = 1
 }