fix(lock): wake monitors on input when powered off by lock (#2572)

The "power off monitors on lock" path relies on wake handlers
(MouseArea/Keys) at Lock.qml's root Scope, which sit outside the
WlSessionLock surface and never receive input while locked. The feature
only appeared to work on compositors that auto-restore output power on
input; compositors that fully tear down the output (e.g. MangoWC
disable_monitor) leave the screen off until blind-unlock.

Add a seat-level IdleMonitor (wlr idle-notify, surface-independent) in
IdleService that restores monitor power on any keyboard/pointer
activity. Gated on isShellLocked + monitorsOff + the setting, so it is
inert unless that path actually powered the monitors off.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

quickshell/Services/IdleService.qml

@@ -138,6 +138,20 @@ Singleton {
         }
     }
 
+    // Wakes monitors powered off by the "power off monitors on lock" path.
+    // Lock.qml's own wake handlers sit outside the session-lock surface and
+    // never receive input, so wake on input via seat-level idle-notify instead.
+    IdleMonitor {
+        id: lockWakeMonitor
+        timeout: 1
+        respectInhibitors: false
+        enabled: root.enabled && root.isShellLocked && root.monitorsOff && SettingsData.lockScreenPowerOffMonitorsOnLock
+        onIsIdleChanged: {
+            if (!isIdle && root.monitorsOff)
+                root.requestMonitorOn();
+        }
+    }
+
     Connections {
         target: root
         function onRequestMonitorOff() {