Silent Task Notifier.

### Describe your improvement idea or feature request

Once a user sets up a task, we should schedule a notifier, silent one most probably, that is triggered 15 minutes as default before the task is due to alert the user that there is an upcoming task before it is due.
We should also include it in the application settings so the user can turn it on and off.

### How would you like to see it implemented?

N/A

### Put here any screenshots or videos (optional)

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### How can we contact you (optional)

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### Would you like to work on this issue?

Yes

### By submitting this issue, I have confirmed that:

- [X] I have starred the repo ⭐ and watched 👀 it on GitHub and followed the contribution guidelines.

The issue does not name files, tests, or entry points. Begin by locating the task setup flow and application settings, then determine where a notification can be scheduled and controlled; done means an upcoming-task alert defaults to 15 minutes before due time and can be turned off in settings.

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