put shell in subdir, and add nix package

shell/bar/notifications/NotificationButton.qml

@@ -0,0 +1,70 @@
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import Qt5Compat.GraphicalEffects
+import Quickshell.Widgets
+import "../.."
+
+Item {
+    id: root
+    required property var bar
+    property var implicitSize: 0
+    readonly property real actualSize: Math.min(root.width, root.height)
+
+    implicitWidth: parent.height
+    implicitHeight: parent.height
+
+    NotificationCenter {
+        id: notificationCenter
+    }
+
+    Rectangle {
+        color: mouseArea.containsMouse ? ShellSettings.colors["primary"] : "transparent"
+        radius: 5
+
+        anchors {
+            fill: parent
+            margins: 1
+        }
+    }
+
+    MouseArea {
+        id: mouseArea
+        hoverEnabled: true
+        anchors.fill: parent
+        onPressed: {
+            if (notificationCenter.visible) {
+                notificationCenter.hide();
+            } else {
+                notificationCenter.show();
+            }
+        }
+    }
+
+    Item {
+        implicitWidth: root.implicitSize
+        implicitHeight: root.implicitSize
+        anchors.centerIn: parent
+
+        layer.enabled: true
+        layer.effect: OpacityMask {
+            source: Rectangle {
+                width: root.actualSize
+                height: root.actualSize
+                color: "white"
+            }
+
+            maskSource: IconImage {
+                implicitSize: root.actualSize
+                source: "root:resources/general/notification.svg"
+            }
+        }
+
+        Rectangle {
+            color: mouseArea.containsMouse ? ShellSettings.colors["inverse_primary"] : ShellSettings.colors["inverse_surface"]
+            anchors.fill: parent
+        }
+    }
+
+    // TODO: notification number overlay
+}