feat(Calendar): integrate CalendarEvent model and enhance calendar functionality

- Added CalendarEvent model to the backend, establishing relationships with the Club model for better event management.
- Updated server.js to include calendarEventRoutes, enabling API access for calendar events.
- Enhanced CalendarView.vue to support custom event creation and management, improving user interaction with the calendar.
- Refactored various components to streamline event handling and improve overall user experience in the calendar interface.
- Updated TODO and DEVELOPMENT documentation to reflect new calendar features and architectural decisions.

backend/controllers/calendarEventController.js

@@ -0,0 +1,42 @@
+import calendarEventService from '../services/calendarEventService.js';
+import { getSafeErrorMessage } from '../utils/errorUtils.js';
+
+export const listClubCalendarEvents = async (req, res) => {
+  try {
+    const { authcode: userToken } = req.headers;
+    const { clubId } = req.params;
+    const { year } = req.query;
+    const events = await calendarEventService.listClubEvents(userToken, clubId, year);
+    res.status(200).json(events);
+  } catch (error) {
+    console.error('[listClubCalendarEvents] - Error:', error);
+    const msg = getSafeErrorMessage(error, 'Fehler beim Laden der Kalender-Events');
+    res.status(error.statusCode || 500).json({ error: msg });
+  }
+};
+
+export const createClubCalendarEvent = async (req, res) => {
+  try {
+    const { authcode: userToken } = req.headers;
+    const { clubId } = req.params;
+    const event = await calendarEventService.createClubEvent(userToken, clubId, req.body);
+    res.status(201).json(event);
+  } catch (error) {
+    console.error('[createClubCalendarEvent] - Error:', error);
+    const msg = getSafeErrorMessage(error, 'Fehler beim Speichern des Kalender-Events');
+    res.status(error.statusCode || 500).json({ error: msg });
+  }
+};
+
+export const deleteClubCalendarEvent = async (req, res) => {
+  try {
+    const { authcode: userToken } = req.headers;
+    const { clubId, eventId } = req.params;
+    const result = await calendarEventService.deleteClubEvent(userToken, clubId, eventId);
+    res.status(200).json(result);
+  } catch (error) {
+    console.error('[deleteClubCalendarEvent] - Error:', error);
+    const msg = getSafeErrorMessage(error, 'Fehler beim Löschen des Kalender-Events');
+    res.status(error.statusCode || 500).json({ error: msg });
+  }
+};