* First pass of implementing Badging API for notifications
* Only show app badge when driven from push notifications
* Display number of unread push notifications instead of just an empty badge
Clear badge via postMessage when notifications page is loaded
* de-dupe some code, update badge counter on each notification click
* remove ids, track open note count instead
* restore optional chaining
* ensure note count doesn't go below 0, and fix event.waitUntil error when clearing badge
* incorporate PR feedback
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