Add calendar routes to backend and frontend; update routing and UI components for calendar feature

frontend/src/router/index.js

@@ -14,6 +14,7 @@ import Timefix from '../views/Timefix.vue'
 import Vacation from '../views/Vacation.vue'
 import Sick from '../views/Sick.vue'
 import Workdays from '../views/Workdays.vue'
+import Calendar from '../views/Calendar.vue'
 
 const router = createRouter({
   history: createWebHistory(import.meta.env.BASE_URL),
@@ -84,6 +85,12 @@ const router = createRouter({
       component: Workdays,
       meta: { requiresAuth: true }
     },
+    {
+      path: '/calendar',
+      name: 'calendar',
+      component: Calendar,
+      meta: { requiresAuth: true }
+    },
     {
       path: '/entries',
       name: 'entries',