Replace HTML buttons with shadcn UI Button components for sign in/sign up

- Added Button import from @/components/ui/button
- Replaced Sign In button with Button variant='outline'
- Replaced Sign Up button with Button variant='default'
- Maintains existing styling and functionality

Fixes #7

Co-authored-by: Tom Phillips <tomphill@users.noreply.github.com>

Author: github-actions[bot]

src/app/layout.tsx

@@ -8,6 +8,7 @@ import {
   SignedOut,
   UserButton,
 } from "@clerk/nextjs";
+import { Button } from "@/components/ui/button";
 import "./globals.css";
 
 const geistSans = Geist({
@@ -41,14 +42,14 @@ export default function RootLayout({
             <div className="flex gap-2">
               <SignedOut>
                 <SignInButton mode="modal">
-                  <button className="px-4 py-2 text-sm font-medium text-gray-700 bg-white border border-gray-300 rounded-md hover:bg-gray-50 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-blue-500">
+                  <Button variant="outline">
                     Sign In
-                  </button>
+                  </Button>
                 </SignInButton>
                 <SignUpButton mode="modal">
-                  <button className="px-4 py-2 text-sm font-medium text-white bg-blue-600 border border-transparent rounded-md hover:bg-blue-700 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-blue-500">
+                  <Button variant="default">
                     Sign Up
-                  </button>
+                  </Button>
                 </SignUpButton>
               </SignedOut>
               <SignedIn>