fix qmllint warnings in systemd/machinectl modules and services

shell/applets/SystemdApplet.qml

@@ -1,3 +1,5 @@
+pragma ComponentBehavior: Bound
+
 import QtQuick
 import "../services" as S
 
@@ -6,6 +8,8 @@ Column {
 
     required property color accentColor
     property bool active: true
+    // Emitted when content resizes; parent can connect to extend panel-close grace.
+    signal contentResized
 
     // Section header: state label + unit count
     Item {
@@ -63,7 +67,7 @@ Column {
             isUser: false
             machineName: ""
             accentColor: root.accentColor
-            onHeightChanged: root.keepPanelOpen?.(300)
+            onHeightChanged: root.contentResized()
         }
     }
 
@@ -139,7 +143,7 @@ Column {
             isUser: true
             machineName: ""
             accentColor: root.accentColor
-            onHeightChanged: root.keepPanelOpen?.(300)
+            onHeightChanged: root.contentResized()
         }
     }