fix(StashModal): 限制仅“full”类型暂存支持导出xml

- 在导出按钮添加条件，仅当 activeItem 类型为 "full" 时显示
- 导出函数增加类型校验，非 "full" 类型显示警告提示
- 调整导出逻辑，确保导出文件始终包含 XML 头声明
- 修复了片段暂存导出不当处理的问题，防止导出无效文件

src/views/editor/components/EditorToolbar/components/StashModal/functionals/index.ts

@@ -363,9 +363,13 @@ export function useStashModal() {
     }
 
     const handleExport = (item: StashItem) => {
+        if (item.type !== 'full') {
+            window.$message?.warning('片段暂存不支持单独导出 XML 文件')
+            return
+        }
         try {
             const singleLineXml = serializeTreeToXml(item.xmlNode, 0, false).replace(/\r?\n\s*/g, '')
-            const xml = item.type === 'full' ? `<?xml version="1.0" encoding="utf-8"?>${singleLineXml}` : singleLineXml
+            const xml = `<?xml version="1.0" encoding="utf-8"?>${singleLineXml}`
             const blob = new Blob([xml], { type: 'application/xml;charset=utf-8;' })
             const safeName = item.name.replace(/[\/\\:*?"<>|]/g, '_')
             openDownloadModal({

src/views/editor/components/EditorToolbar/components/StashModal/index.vue

@@ -127,7 +127,7 @@
                                 </template>
                                 效果预览
                             </CommonButton>
-                            <CommonButton size="small" secondary @click="handleExport(activeItem)">
+                            <CommonButton v-if="activeItem.type === 'full'" size="small" secondary @click="handleExport(activeItem)">
                                 <template #icon>
                                     <n-icon><DownloadOutline /></n-icon>
                                 </template>