Add Notification System for Event Updates

Implement a notification system that informs users when:

1. - A new vote is added to their event.

2. An event is finalized.

3. Someone comments on an event.

4. This helps improve user engagement and awareness of important updates, especially in collaborative planning.

🎯 Objective:
Display non-intrusive toast or bell-style notifications in the UI.

Real-time updates via WebSockets (you already use WebSockets for voting).

Show unread notification count in navbar.

Option to mark all as read.