fix: 去掉 background.js 的 JSON 调试下载

该下载在 PPTX 转化前触发，转化失败时用户只看到 JSON。

web-to-ppt/background.js

@@ -146,17 +146,7 @@ chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
       assertCaptureableTab(tab);
       const data = await captureCurrentTab(tab, settings);
       lastCaptureData = data;
-      // 保存 JSON 供调试
-      try {
-        const json = JSON.stringify(data, null, 2);
-        const encoded = btoa(unescape(encodeURIComponent(json)));
-        const title = data.source?.title || 'debug';
-        const safe = title.replace(/[\\/:*?"<>|]+/g, '-').slice(0, 32);
-        chrome.downloads.download({
-          url: 'data:application/json;base64,' + encoded,
-          filename: 'web-to-ppt/' + safe + '-' + Date.now() + '.json'
-        });
-      } catch(e) {}
+
       return { ok: true, actualViewportWidth: data.source?.actualViewportWidth };
     })()
       .then(sendResponse)