update slides: add course numbers to headers, widen stripe pattern

- add course number (223015b/c) to all slide headers
- widen klausur diagonal stripes from 20/40px to 40/80px
- expand termin-1 with analog vs digital media content
- rename wtf files exercise to hex files

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

@@ -3,7 +3,7 @@ marp: true
 theme: gaia
 paginate: true
 backgroundColor: #fff
-header: "Dateiformate, Schnittstellen, Speichermedien & Distributionswege"
+header: "Dateiformate, Schnittstellen, Speichermedien & Distributionswege (223015b)"
 footer: "Michael Czechowski – HdM Stuttgart – WS 2025/26"
 title: Dateiformate, Schnittstellen, Speichermedien & Distributionswege
 ---
@@ -52,9 +52,9 @@ section.klausur {
   background: repeating-linear-gradient(
     135deg,
     #e3f2fd,
-    #e3f2fd 20px,
-    #fff 20px,
-    #fff 40px
+    #e3f2fd 40px,
+    #fff 40px,
+    #fff 80px
   ) !important;
 }
 section.klausur footer {