fix: 下载移到 background.js 执行，和原插件一致

web-to-ppt/background.js

@@ -259,6 +259,18 @@ chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
     return true;
   }
 
+  // 下载 PPTX（由 popup 调用，background 执行下载）
+  if (message?.type === "WEB_TO_PPT_DOWNLOAD") {
+    (async () => {
+      const dataUrl = 'data:application/vnd.openxmlformats-officedocument.presentationml.presentation;base64,' + message.base64;
+      await chrome.downloads.download({ url: dataUrl, filename: message.filename });
+      return { ok: true };
+    })()
+      .then(sendResponse)
+      .catch(error => sendResponse({ ok: false, error: error.message || String(error) }));
+    return true;
+  }
+
   return false;
 });