[Feature/Improvement] Notification Controls

**Purpose:** To be able to pause/play and view the timer countdown on the lockscreen or in the notification panel when using other apps

**More details:** Like many music players on mobile, the ability to pause/play and view the timer countdown in the notifications

Look for notification handling code in the Flutter project, likely using packages like flutter_local_notifications. Examine how the timer state is currently managed and displayed. The goal is to add play/pause controls and a live countdown to the persistent notification, similar to music player apps. Check existing timer logic to see how state updates can be broadcast to the notification.

Scritto dal modello di indicizzazione a partire dal testo della issue.