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

Widgets/NotificationPopupNative.qml

@@ -0,0 +1,104 @@
+import QtQuick
+import QtQuick.Controls
+import Quickshell
+import Quickshell.Widgets
+import Quickshell.Wayland
+import "../Common"
+import "../Services"
+
+PanelWindow {
+    id: notificationPopup
+    
+    visible: NotificationService.popups.length > 0
+    
+    WlrLayershell.layer: WlrLayershell.Overlay
+    WlrLayershell.exclusiveZone: -1
+    WlrLayershell.keyboardFocus: WlrKeyboardFocus.None
+    
+    color: "transparent"
+    
+    anchors {
+        top: true
+        right: true
+    }
+    
+    margins {
+        top: Theme.barHeight
+        right: 16
+    }
+    
+    implicitWidth: 400
+    implicitHeight: notificationList.height + 32
+    
+    Column {
+        id: notificationList
+        anchors.top: parent.top
+        anchors.right: parent.right
+        anchors.topMargin: 16
+        anchors.rightMargin: 16
+        spacing: Theme.spacingM
+        width: 380
+        
+        Repeater {
+            model: NotificationService.popups
+            
+            delegate: NotificationItem {
+                required property var modelData
+                notificationWrapper: modelData
+                
+                // Entry animation
+                transform: [
+                    Translate {
+                        id: slideTransform
+                        x: notificationPopup.visible ? 0 : 400
+                        
+                        Behavior on x {
+                            NumberAnimation {
+                                duration: Theme.mediumDuration
+                                easing.type: Theme.emphasizedEasing
+                            }
+                        }
+                    },
+                    Scale {
+                        id: scaleTransform
+                        origin.x: parent.width
+                        origin.y: 0
+                        xScale: notificationPopup.visible ? 1.0 : 0.95
+                        yScale: notificationPopup.visible ? 1.0 : 0.8
+                        
+                        Behavior on xScale {
+                            NumberAnimation {
+                                duration: Theme.mediumDuration
+                                easing.type: Theme.emphasizedEasing
+                            }
+                        }
+                        
+                        Behavior on yScale {
+                            NumberAnimation {
+                                duration: Theme.mediumDuration
+                                easing.type: Theme.emphasizedEasing
+                            }
+                        }
+                    }
+                ]
+                
+                opacity: notificationPopup.visible ? 1.0 : 0.0
+                
+                Behavior on opacity {
+                    NumberAnimation {
+                        duration: Theme.mediumDuration
+                        easing.type: Theme.emphasizedEasing
+                    }
+                }
+            }
+        }
+    }
+    
+    // Smooth height animation
+    Behavior on implicitHeight {
+        NumberAnimation {
+            duration: Theme.mediumDuration
+            easing.type: Theme.emphasizedEasing
+        }
+    }
+}