begin adding shadcn components for frontend

frontend/src/App.css

@@ -18,3 +18,9 @@ body {
   background-color: var(--background-color);
   color: var(--text-color);
 }
+
+@layer base {
+  :root {
+    --radius: 0.5rem;
+  }
+}

frontend/src/components/ui/button.tsx

@@ -0,0 +1,57 @@
+import * as React from "react"
+import { Slot } from "@radix-ui/react-slot"
+import { cva, type VariantProps } from "class-variance-authority"
+
+import { cn } from "@/lib/utils"
+
+const buttonVariants = cva(
+  "inline-flex items-center justify-center gap-2 whitespace-nowrap rounded-md text-sm font-medium transition-colors focus-visible:outline-none focus-visible:ring-1 focus-visible:ring-zinc-950 disabled:pointer-events-none disabled:opacity-50 [&_svg]:pointer-events-none [&_svg]:size-4 [&_svg]:shrink-0 dark:focus-visible:ring-zinc-300",
+  {
+    variants: {
+      variant: {
+        default:
+          "bg-zinc-900 text-zinc-50 shadow hover:bg-zinc-900/90 dark:bg-zinc-50 dark:text-zinc-900 dark:hover:bg-zinc-50/90",
+        destructive:
+          "bg-red-500 text-zinc-50 shadow-sm hover:bg-red-500/90 dark:bg-red-900 dark:text-zinc-50 dark:hover:bg-red-900/90",
+        outline:
+          "border border-zinc-200 bg-white shadow-sm hover:bg-zinc-100 hover:text-zinc-900 dark:border-zinc-800 dark:bg-zinc-950 dark:hover:bg-zinc-800 dark:hover:text-zinc-50",
+        secondary:
+          "bg-zinc-100 text-zinc-900 shadow-sm hover:bg-zinc-100/80 dark:bg-zinc-800 dark:text-zinc-50 dark:hover:bg-zinc-800/80",
+        ghost: "hover:bg-zinc-100 hover:text-zinc-900 dark:hover:bg-zinc-800 dark:hover:text-zinc-50",
+        link: "text-zinc-900 underline-offset-4 hover:underline dark:text-zinc-50",
+      },
+      size: {
+        default: "h-9 px-4 py-2",
+        sm: "h-8 rounded-md px-3 text-xs",
+        lg: "h-10 rounded-md px-8",
+        icon: "h-9 w-9",
+      },
+    },
+    defaultVariants: {
+      variant: "default",
+      size: "default",
+    },
+  }
+)
+
+export interface ButtonProps
+  extends React.ButtonHTMLAttributes<HTMLButtonElement>,
+    VariantProps<typeof buttonVariants> {
+  asChild?: boolean
+}
+
+const Button = React.forwardRef<HTMLButtonElement, ButtonProps>(
+  ({ className, variant, size, asChild = false, ...props }, ref) => {
+    const Comp = asChild ? Slot : "button"
+    return (
+      <Comp
+        className={cn(buttonVariants({ variant, size, className }))}
+        ref={ref}
+        {...props}
+      />
+    )
+  }
+)
+Button.displayName = "Button"
+
+export { Button, buttonVariants }