Both the `/notifications` inbox and the Settings -> Notifications
section used to read as plain "Notifications" in every nav surface, so
the user-card dropdown and the settings sidebar looked like two pointers
at the same destination. Rename the inbox to "Notification Center" and
the settings section to "Notification channels"; add a small breadcrumb
to either surface so the user always knows which page they landed on
and can jump to the sibling in one tap.
Locale parity across de / en / es / fr / it / pl.
