feat: Add manual event notification endpoint for admins

- POST /api/events/:eventId/notify - send notifications from admin's email
- sendSingleEventNotification() uses admin's primary email account
- getSenderAccountByUserId() to get admin's email credentials

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

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

src/routes/event.routes.js

@@ -69,4 +69,14 @@ router.delete(
   eventController.deleteEvent
 );
 
+/**
+ * POST /api/events/:eventId/notify - Odoslať notifikácie priradeným používateľom (iba admin)
+ */
+router.post(
+  '/:eventId/notify',
+  requireAdmin,
+  validateParams(eventIdSchema),
+  eventController.sendEventNotification
+);
+
 export default router;