fix: 商机改为已流失时前端自动清空列收时间再提交

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/views/mobile/MiniBusinessForm.vue

@@ -78,6 +78,7 @@ async function handleQuickCreate() {
 
 async function handleSubmit() {
   if (!form.value.customer_id) { ElMessage.warning('请选择客户'); return }
+  if (form.value.status === '已流失') form.value.expected_revenue_date = ''
   submitLoading.value = true
   try {
     if (isEdit.value) {