feat: Add autofocus on sign up, sign in form

src/components/Login/LoginForm.jsx

@@ -41,6 +41,7 @@ const LoginForm = () => {
           placeholder="아이디"
           value={username}
           onChange={(e) => setUsername(e.target.value)}
+          autoFocus
         />
       </div>
       <div className="formInput">

src/components/Signup/SignupForm.jsx

@@ -45,6 +45,7 @@ const SignupForm = () => {
           placeholder="아이디"
           value={username}
           onChange={(e) => setUsername(e.target.value)}
+          autoFocus
         />
       </div>
       <div className="formInput">