♻️ Rework authentication

- Move login endpoint `/login` to `/auth/login`
- Add logout route `/auth/logout`
- Add `/api/token` endpoint and `?token=` query parameter for auth
- Refactor `auth.js`

src/views/LoginView.vue

@@ -1,7 +1,7 @@
 <template>
   <div class="login">
     <h1>Timetable V2</h1>
-    <form action="/login" method="POST">
+    <form action="/auth/login" method="POST">
       <input
         type="password"
         name="password"