fix: render PDF from attached DOM container to avoid blank pages

public/index.html

@@ -500,22 +500,43 @@ async function downloadPdf(){
     alert('PDF-Export-Bibliothek nicht geladen.');
     return;
   }
+
   const root = document.createElement('div');
+  root.style.position = 'fixed';
+  root.style.left = '0';
+  root.style.top = '0';
+  root.style.width = '210mm';
+  root.style.minHeight = '297mm';
   root.style.background = '#fff';
-  root.style.padding = '8px';
+  root.style.padding = '8mm';
+  root.style.zIndex = '-1';
+  root.style.opacity = '0.01';
+  root.style.pointerEvents = 'none';
   root.innerHTML = app.innerHTML;
+
   root.querySelectorAll('.card-actions,.card-action-btn,button,[data-edit-all]').forEach(el => el.remove());
+  root.querySelectorAll('.exercise-container').forEach(el => { el.style.pageBreakAfter = 'always'; });
+  root.querySelectorAll('.card-size').forEach(el => {
+    el.style.boxShadow = 'none';
+    el.style.margin = '0 auto 10mm auto';
+  });
+
+  document.body.appendChild(root);
 
   const opt = {
-    margin: [8, 8, 8, 8],
+    margin: [5, 5, 5, 5],
     filename: `coachingcards-${new Date().toISOString().slice(0,10)}.pdf`,
-    image: { type: 'jpeg', quality: 0.96 },
-    html2canvas: { scale: 2, useCORS: true, backgroundColor: '#ffffff' },
+    image: { type: 'jpeg', quality: 0.98 },
+    html2canvas: { scale: 2, useCORS: true, backgroundColor: '#ffffff', logging: false },
     jsPDF: { unit: 'mm', format: 'a4', orientation: 'portrait' },
     pagebreak: { mode: ['css', 'legacy'] }
   };
 
+  try {
     await window.html2pdf().set(opt).from(root).save();
+  } finally {
+    root.remove();
+  }
 }
 
 async function syncActiveJob(){