Notification: add auto-dismiss and "pause" UI indicator

[humitos]

In #375 we added auto-dismiss after 5s. It would be good to add a bottom border expressing the progress of the countdown.

Also, instead of resetting the timer when hovering it would be good to pause it.

[ericholscher]

This could be a nice place for testing shoelace which can do this natively: https://shoelace.style/components/alert#countdown

[humitos]

I'm going to close this issue since we are going to re-design the whole UI and this is already considered there. See #574 for more information.