Light the screen (dimmed) while a Notification's Toast shows

An Off screen turns on dimmed for the Toast's duration so the user can
see what beeped. It isn't user activity: the timeouts aren't restarted,
and a key pressed meanwhile reaches the App.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/main.cpp

@@ -79,6 +79,7 @@ void setup() {
     power = new PowerService(settings);
     clockService = new ClockService(settings, bus);
     notifier = new Notifier(bus, settings);
+    notifier->onShow = [](uint32_t now, uint32_t until) { power->onNotification(now, until); };
     services.add(*power);
     services.add(*clockService);
     services.add(*battery);