feat: Add daily event notification emails via cron job

- Add node-cron for scheduled tasks
- Create cron/calendar structure with:
  - email-template.js: HTML email template for event notifications
  - event-notifier.js: Logic to query tomorrow's events and send emails
  - index.js: Cron scheduler (runs daily at configurable time)
- Send notifications via JMAP using sender email from database
- Add admin endpoint POST /api/admin/trigger-notifications for testing
- Add env variables: NOTIFICATION_TIME, NOTIFICATION_SENDER_EMAIL

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cron/index.js

@@ -0,0 +1,17 @@
+import { logger } from '../utils/logger.js';
+import { startCalendarNotificationCron, triggerEventNotifications } from './calendar/index.js';
+
+/**
+ * Start all cron jobs
+ */
+export const startAllCronJobs = () => {
+  logger.info('=== Inicializujem cron jobs ===');
+
+  // Calendar event notifications
+  startCalendarNotificationCron();
+
+  logger.info('=== Všetky cron jobs inicializované ===');
+};
+
+// Export individual functions for testing/manual triggers
+export { triggerEventNotifications };