fix klausur gradient for pdf printing in termin 0,3,4,5

- add !important to repeating-linear-gradient for proper pdf export

courses/223015b/slides/2025-12-19-termin-0-intro.md

@@ -55,7 +55,7 @@ section.klausur {
     #e3f2fd 40px,
     #fff 40px,
     #fff 80px
-  );
+  ) !important;
 }
 section.aufgabe {
   background: #e3f2fd !important;