After unlocking the screen (startup lock or wake from sleep), the desktop
showed Hyprland's background color instead of the wallpaper.
WallpaperBackground disables QML updates via updatesEnabled after a 1-second
settle timer. While WlSessionLock is active, Hyprland does not composite the
background layer, so when the lock is released it needs a fresh Wayland buffer
— but none is committed because the render loop is already paused.
The previous attempt used SessionService.sessionUnlocked, which is unreliable
for the startup lock case: DMSService is not yet connected when lock() is
called at startup, so notifyLoginctl is a no-op and the loginctl state never
transitions, meaning sessionUnlocked never fires.
Fix by tracking the shell lock state directly from Lock.qml's shouldLock via
a new IdleService.isShellLocked property. WallpaperBackground watches this and
re-enables rendering for 1 second on unlock, ensuring a fresh buffer is
committed to Wayland before the compositor resumes displaying the layer.
Add ability to immediately power off monitors when the lock screen
activates, controlled by a new setting "Power off monitors on lock".
Uses a 100ms polling timer to detect when the session lock actually
becomes active, then invokes compositor-specific DPMS commands.
For niri, uses the new power-off-monitors action via niri msg CLI
with socket fallback.
Wake on input: first input after lock arms wake, second input
actually powers monitors back on while keeping the lock screen visible.
Closes#1157
