Replace QDBusConnection::systemBus() with QDBusConnection::sessionBus()
when creating the org.ukui.ScreenSaver interface and connecting
Lock/Unlock signals so notifications are tied to the user session
Record lock time, duration and count in CustomWidget and show a
lock-info overlay. setPaintingEnabled now logs lock/unlock times and
increments lock count. Emit screenLocked/screenUnlocked signals in
ScreenLockDetector. Minor UI and whitespace cleanup.