chore: update Tailwind CSS from 3.4.15, to 4.1.11

- Changed the PostCSS configuration to use '@tailwindcss/postcss' instead of 'tailwindcss'.
- Deleted the Tailwind configuration file as it is no longer needed.

components/ui/card.tsx

@@ -9,7 +9,7 @@ const Card = React.forwardRef<
   <div
     ref={ref}
     className={cn(
-      "rounded-xl border bg-card text-card-foreground shadow",
+      "rounded-xl border bg-card text-card-foreground shadow-sm",
       className
     )}
     {...props}