Deliver notifications in-app (mobile push and web) in addition to SMS and email

Problem:

Flight event notifications are only delivered via SMS and email. Notifications aren't linked into the app and require app-switching to read.

Desired outcome:

Users can choose "in-app" as a notification delivery channel. On mobile this means native push; on web, notifications surface inside the app with a click-through to the relevant view.

Proposed change:

Extend Notifications configuration to include an "in-app" option per event type. Notifications deep-link to the flying page with the source aircraft selected.