RequireAuth 컴포넌트 추가

frontend/src/auth/RequireAuth.tsx

+import React, { FC } from "react";
+import { Navigate, useLocation } from "react-router-dom";
+import { useAuth } from "./auth.context";
+
+export const RequireAuth: FC<{ children: JSX.Element }> = ({ children }) => {
+  const { user } = useAuth();
+  const location = useLocation();
+
+  if (!user.isLoggedIn) {
+    return (
+      <Navigate to={"/login"} state={{ from: location.pathname }} replace />
+    );
+  }
+  return children;
+};