Add speed formatting to display appropriate units (KB/s, MB/s)

public/app.js

@@ -879,7 +879,7 @@ function createDownloadCard(download) {
   }
   
   if (download.speed && download.speed > 0) {
-    const speed = createDetailItem('Speed', download.speed);
+    const speed = createDetailItem('Speed', formatSpeed(download.speed));
     details.appendChild(speed);
   }
   
@@ -936,6 +936,21 @@ function createDownloadCard(download) {
   return card;
 }
 
+function formatSpeed(bytesPerSecond) {
+  if (!bytesPerSecond || bytesPerSecond === 0) return '0 B/s';
+  
+  const units = ['B/s', 'KB/s', 'MB/s', 'GB/s'];
+  let value = bytesPerSecond;
+  let unitIndex = 0;
+  
+  while (value >= 1024 && unitIndex < units.length - 1) {
+    value /= 1024;
+    unitIndex++;
+  }
+  
+  return `${value.toFixed(2)} ${units[unitIndex]}`;
+}
+
 function createDetailItem(label, value) {
   const item = document.createElement('div');
   item.className = 'detail-item';