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/controllers/admin.controller.js

@@ -1,6 +1,7 @@
 import * as adminService from '../services/admin.service.js';
 import * as statusService from '../services/status.service.js';
 import { logUserCreation, logRoleChange } from '../services/audit.service.js';
+import { triggerEventNotifications } from '../cron/index.js';
 
 /**
  * Vytvorenie nového usera s automatic temporary password (admin only)
@@ -160,3 +161,21 @@ export const getServerStatus = async (req, res, next) => {
     next(error);
   }
 };
+
+/**
+ * Manually trigger event notifications (admin only, for testing)
+ * POST /api/admin/trigger-notifications
+ */
+export const triggerNotifications = async (req, res, next) => {
+  try {
+    const stats = await triggerEventNotifications();
+
+    res.status(200).json({
+      success: true,
+      data: stats,
+      message: `Notifikácie odoslané: ${stats.sent}, neúspešné: ${stats.failed}, preskočené: ${stats.skipped}`,
+    });
+  } catch (error) {
+    next(error);
+  }
+};