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/services/power_service.h

@@ -19,6 +19,9 @@ class PowerService : public Service {
     // Call for every key press before routing it. Returns true if the key must not reach the App.
     bool onKey(uint32_t nowMs) { return policy_.activity(nowMs); }
 
+    // A Toast is showing until untilMs: light an Off screen (dimmed) so it can be read.
+    void onNotification(uint32_t nowMs, uint32_t untilMs) { policy_.notify(nowMs, untilMs); }
+
     ScreenState screen() const { return applied_; }
 
    private: