Revert "fix: backgroundUrls 从 const 改为 let，允许 SVG 赋值"

This reverts commit 33fc8b06d6.

web-to-ppt/background.js

@@ -146,6 +146,17 @@ chrome.runtime.onMessage.addListener((message, sender, sendResponse) => {
       assertCaptureableTab(tab);
       const data = await captureCurrentTab(tab, settings);
       lastCaptureData = data;
+      // 调试：保存 JSON 到 Downloads
+      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);
+        await 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)

web-to-ppt/capture.js

@@ -984,6 +984,20 @@
     const afterNode = pseudoElementToCaptureNode(element, "::after", clientRect, assetUrls, ownClip, childContext);
     pushCaptureChild(children, afterNode);
 
+    // SVG → 序列化为 data URL 图片
+    if ((element.tagName === "SVG" || element.tagName === "svg") && !backgroundUrls.length) {
+      try {
+        const svgClone = element.cloneNode(true);
+        if (!svgClone.getAttribute('xmlns')) svgClone.setAttribute('xmlns', 'http://www.w3.org/2000/svg');
+        const svgStr = new XMLSerializer().serializeToString(svgClone);
+        const svgDataUrl = 'data:image/svg+xml;base64,' + btoa(unescape(encodeURIComponent(svgStr)));
+        backgroundUrls = [svgDataUrl];
+        console.log('[WebToPPT] SVG captured:', (element.className || element.id || '').slice(0, 30), 'size:', svgStr.length);
+      } catch (e) {
+        console.warn('[WebToPPT] SVG capture failed:', e.message, element.tagName, (element.className || '').slice(0, 30));
+      }
+    }
+
     const type = element.tagName === "IMG" || backgroundUrls.length ? "RECTANGLE" : "FRAME";
     return {
       id: `node-${++nodeCounter}`,