Notification: add transparency slider (implements #586)

Modules/Notification/Notification.qml

@@ -185,9 +185,9 @@ Variants {
             Layout.maximumHeight: Layout.preferredHeight
 
             radius: Style.radiusL
-            border.color: Color.mOutline
+            border.color: Qt.alpha(Color.mOutline, Settings.data.notifications.backgroundOpacity || 1.0)
             border.width: Style.borderS
-            color: Color.mSurface
+            color: Qt.alpha(Color.mSurface, Settings.data.notifications.backgroundOpacity || 1.0)
 
             // Optimized progress bar container
             Rectangle {
@@ -212,12 +212,14 @@ Variants {
                 width: parent.availableWidth * model.progress
 
                 color: {
+                  var baseColor
                   if (model.urgency === NotificationUrgency.Critical || model.urgency === 2)
-                    return Color.mError
+                    baseColor = Color.mError
                   else if (model.urgency === NotificationUrgency.Low || model.urgency === 0)
-                    return Color.mOnSurface
+                    baseColor = Color.mOnSurface
                   else
-                    return Color.mPrimary
+                    baseColor = Color.mPrimary
+                  return Qt.alpha(baseColor, Settings.data.notifications.backgroundOpacity || 1.0)
                 }
 
                 antialiasing: true

Modules/Settings/Tabs/NotificationsTab.qml

@@ -72,6 +72,27 @@ ColumnLayout {
       onToggled: checked => Settings.data.notifications.overlayLayer = checked
     }
 
+    // Background Opacity
+    ColumnLayout {
+      spacing: Style.marginXXS
+      Layout.fillWidth: true
+
+      NLabel {
+        label: I18n.tr("settings.notifications.settings.background-opacity.label")
+        description: I18n.tr("settings.notifications.settings.background-opacity.description")
+      }
+
+      NValueSlider {
+        Layout.fillWidth: true
+        from: 0
+        to: 100
+        stepSize: 1
+        value: Settings.data.notifications.backgroundOpacity * 100
+        onMoved: value => Settings.data.notifications.backgroundOpacity = value / 100
+        text: Math.round(Settings.data.notifications.backgroundOpacity * 100) + "%"
+      }
+    }
+
     // OSD settings moved to the dedicated OSD tab
   }