Add calendar feature: Integrate calendarRouter and CalendarEvent model, enhance CalendarView with API interactions for event management, and update localization files for error handling in both English and German. This update improves the calendar functionality and user experience.

backend/routers/calendarRouter.js

@@ -0,0 +1,14 @@
+import { Router } from 'express';
+import { authenticate } from '../middleware/authMiddleware.js';
+import calendarController from '../controllers/calendarController.js';
+
+const router = Router();
+
+// All routes require authentication
+router.get('/events', authenticate, calendarController.getEvents);
+router.get('/events/:id', authenticate, calendarController.getEvent);
+router.post('/events', authenticate, calendarController.createEvent);
+router.put('/events/:id', authenticate, calendarController.updateEvent);
+router.delete('/events/:id', authenticate, calendarController.deleteEvent);
+
+export default router;