feat: add utility function for class merging with Tailwind and clsx

Introduce `cn` utility function to simplify class name manipulation by combining `clsx` and `tailwind-merge`.

frontend/src/lib/utils.ts

@@ -0,0 +1,6 @@
+import { clsx, type ClassValue } from "clsx"
+import { twMerge } from "tailwind-merge"
+
+export function cn(...inputs: ClassValue[]) {
+  return twMerge(clsx(inputs))
+}