Create push notifications

[TheTeaCat]

When:

• Timer finishes
• Timer is finishing in 1hr
• Timer is finishing today, for timers longer than 24hrs

Blocked by #4

This would likely be a "premium" feature as it'd require backend infrastructure.

[TheTeaCat]

This is more complicated than anticipated. Removing from v1.0.0 milestone.

[TheTeaCat]

We could use the periodic background sync API for this:

https://web.dev/periodic-background-sync/

However it has about 72% global support right now (it's missing on Firefox and Safari):

https://caniuse.com/?search=Periodic%20Background%20Sync%20API

[TheTeaCat]

The push API is only marginally better (has firefox support)

https://caniuse.com/?search=push%20api