Fix blank PDF by using temporary DOM element for rendering

src/components/Tutorials.astro

@@ -60,8 +60,17 @@ function downloadPDF(elementId, title) {
         jsPDF:        { unit: 'mm', format: 'a4', orientation: 'portrait' }
     };
     
+    // Create temporary element
+    const worker = document.createElement('div');
+    worker.innerHTML = html;
+    worker.style.position = 'absolute';
+    worker.style.left = '-9999px';
+    document.body.appendChild(worker);
+    
     // PDF generieren
-    html2pdf().set(opt).from(html).save();
+    html2pdf().set(opt).from(worker).save().then(() => {
+        document.body.removeChild(worker);
+    });
 }
 </script>