Bar widgets: modular loading refactoring via BarWidgetRegistry+NWidgetLoader

- Hot reload is working again.
- Should also be more memory efficient on multi monitors.

Modules/Bar/Widgets/SidePanelToggle.qml

@@ -1,9 +1,14 @@
 import Quickshell
 import qs.Commons
 import qs.Widgets
+import qs.Services
 
 NIconButton {
-  id: sidePanelToggle
+  id: root
+
+  property ShellScreen screen
+  property real scaling: ScalingService.scale(screen)
+
   icon: "widgets"
   tooltipText: "Open Side Panel"
   sizeMultiplier: 0.8
@@ -14,5 +19,5 @@ NIconButton {
   colorBorderHover: Color.transparent
 
   anchors.verticalCenter: parent.verticalCenter
-  onClicked: sidePanel.toggle(screen)
+  onClicked: PanelService.getPanel("sidePanel")?.toggle(screen)
 }