Timer ending is not obvious enough

From what I understand, when a timer runs out, it vibrates once and then resets to 00:00.

• It should vibrate repeatedly until dismissed so you don't ignore it and have your water boil over or similar (you may be timing something very urgent)
• There should be some sort of message that your timer expired so if you look at it a minute late you remember what happened

I also think it should not clear the timer value, but maybe that would work best after implementing my idea (https://github.com/JF002/InfiniTime/issues/390#issuecomment-846558561) to save timer presets. It would then show something like 05:00 after your 5 minute timer ended, and you would press the back button to get to a screen that lists all your timers, similar to the Pebble timer app.

Start by locating the timer expiration, displayed timer value, and vibration handling in the firmware, then review the timer-presets discussion in issue #390. Done means an expired timer remains identifiable, signals repeatedly until dismissed, and preserves the relevant timer value without disrupting navigation.