refactor: remove demo auth notice from login page

frontend/src/pages/LoginPage.jsx

@@ -96,12 +96,6 @@ const LoginPage = () => {
             </Link>
           </p>
         </div>
-
-        <div className="mt-6 p-4 bg-yellow-50 border border-yellow-200 rounded-md">
-          <p className="text-xs text-yellow-800">
-            <strong>Demo:</strong> Enter any email and password to sign in (mock auth)
-          </p>
-        </div>
       </div>
     </div>
   );