fix: 修复工作流开始表单文案清空回退

- 保留标题和说明的显式空值

- 同步运行页与后端解析逻辑

easyflow-ui-usercenter/app/src/views/ai/workflow/components/WorkflowForm.vue

@@ -37,11 +37,14 @@ const submitLoading = ref(false);
 const startFormMeta = computed(() => {
   const meta = props.workflowParams?.startFormMeta || {};
   return {
-    title: String(meta.title || '').trim() || props.workflowParams?.title || '',
+    title:
+      meta.title == null
+        ? props.workflowParams?.title || ''
+        : String(meta.title).trim(),
     description:
-      String(meta.description || '').trim() ||
-      props.workflowParams?.description ||
-      '',
+      meta.description == null
+        ? props.workflowParams?.description || ''
+        : String(meta.description).trim(),
     submitText: String(meta.submitText || '').trim() || $t('button.run'),
   };
 });