fix: 修复图片压缩工具下载功能

修复图片压缩后无法下载的问题。原代码在预览图片加载完成时立即释放了URL，导致下载链接失效。

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: chao5go

tools/image-compressor/app.html

@@ -265,9 +265,12 @@ <h1>图片压缩工具</h1>
             const quality = parseFloat(qualityInput.value);
             canvas.toBlob((blob) => {
                 if (!blob) return;
+                // 释放之前的URL
+                if (downloadLink.href && downloadLink.href !== '#') {
+                    URL.revokeObjectURL(downloadLink.href);
+                }
                 const url = URL.createObjectURL(blob);
                 const previewImg = new Image();
-                previewImg.onload = () => URL.revokeObjectURL(url);
                 previewImg.src = url;
                 preview.innerHTML = '';
                 preview.appendChild(previewImg);