Re-add root .gitignore, add missing src/lib/utils.ts shadcn helper

.gitignore

@@ -0,0 +1 @@
+.env

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));
+}