Migrate notification system to native Quickshell NotificationServer API

- Replace custom NotificationGroupingService with native NotificationService
- Implement proper image/icon priority system (notification image → app icon → fallback)
- Add NotificationItem with image layering and elegant emoji fallbacks
- Create native popup and history components with smooth animations
- Fix Discord/Vesktop avatar display issues
- Clean up legacy notification components and demos
- Improve Material Design 3 theming consistency

Tests/NotificationNativeDemo.qml

@@ -0,0 +1,97 @@
+import QtQuick
+import QtQuick.Controls
+import QtQuick.Layouts
+import "../Common"
+import "../Services"
+import "../Widgets"
+
+ApplicationWindow {
+    id: demoWindow
+    width: 800
+    height: 600
+    visible: true
+    title: "Native Notification System Demo"
+    
+    color: Theme.background
+    
+    Column {
+        anchors.centerIn: parent
+        spacing: Theme.spacingL
+        
+        Text {
+            anchors.horizontalCenter: parent.horizontalCenter
+            text: "Native Notification System Demo"
+            font.pixelSize: Theme.fontSizeXLarge
+            color: Theme.surfaceText
+            font.weight: Font.Bold
+        }
+        
+        Text {
+            anchors.horizontalCenter: parent.horizontalCenter
+            text: "This demo uses Quickshell's native NotificationServer"
+            font.pixelSize: Theme.fontSizeMedium
+            color: Theme.onSurfaceVariant
+        }
+        
+        Row {
+            anchors.horizontalCenter: parent.horizontalCenter
+            spacing: Theme.spacingL
+            
+            Button {
+                text: "Show Popups"
+                onClicked: notificationPopup.visible = true
+            }
+            
+            Button {
+                text: "Show History"
+                onClicked: notificationHistory.notificationHistoryVisible = true
+            }
+            
+            Button {
+                text: "Clear All"
+                onClicked: NotificationService.clearAllNotifications()
+            }
+        }
+        
+        Column {
+            anchors.horizontalCenter: parent.horizontalCenter
+            spacing: Theme.spacingM
+            
+            Text {
+                text: `Total Notifications: ${NotificationService.notifications.length}`
+                font.pixelSize: Theme.fontSizeMedium
+                color: Theme.surfaceText
+            }
+            
+            Text {
+                text: `Active Popups: ${NotificationService.popups.length}`
+                font.pixelSize: Theme.fontSizeMedium
+                color: Theme.surfaceText
+            }
+        }
+        
+        Text {
+            width: 600
+            anchors.horizontalCenter: parent.horizontalCenter
+            text: "Instructions:\n" +
+                  "• Send notifications from other applications (Discord, etc.)\n" +
+                  "• Use 'notify-send' command to test\n" +
+                  "• Notifications will appear automatically in the popup\n" +
+                  "• Images from Discord/Vesktop will show as avatars\n" +
+                  "• App icons are automatically detected"
+            font.pixelSize: Theme.fontSizeSmall
+            color: Theme.onSurfaceVariant
+            wrapMode: Text.WordWrap
+        }
+    }
+    
+    // Native notification popup
+    NotificationPopupNative {
+        id: notificationPopup
+    }
+    
+    // Native notification history
+    NotificationHistoryNative {
+        id: notificationHistory
+    }
+}