Use thumbnail url from backend everywhere, closes #66

src/components/VideoCard.tsx

@@ -40,7 +40,10 @@ export function VideoCard({
                             height: "auto",
                             width: "170px",
                         }}
-                        src={`${api.assetUrl()}/thumbnail/l_${lecture.id}.jpg`}
+                        src={
+                            lecture.thumbnail_url ??
+                            `${api.assetUrl()}/thumbnail/l_${lecture.id}.jpg`
+                        }
                         alt="Vorschaubild"
                     />
                     <div className="col-4">
@@ -72,7 +75,10 @@ export function VideoCard({
                         <img
                             width="170"
                             height="100"
-                            src={`${api.assetUrl()}/thumbnail/l_${lecture.id}.jpg`}
+                            src={
+                                lecture.thumbnail_url ??
+                                `${api.assetUrl()}/thumbnail/l_${lecture.id}.jpg`
+                            }
                             alt="Vorschaubild"
                         />
                     </li>