✨ Calculate number of columns depending on screen size

lib/mixing_tab.dart

@@ -12,7 +12,7 @@ class _MixingTabState extends State<MixingTab> {
   @override
   Widget build(BuildContext context) {
     double screenWidth = MediaQuery.of(context).size.width;
-    int cols = screenWidth > 550 ? 2 : 1;
+    int cols = 1 + (screenWidth ~/ 550);
     int cardHeight = 110;
 
     return SizedBox.expand(