feat(osd): add volume osd popup window

windows/Volume.qml

@@ -0,0 +1,52 @@
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import Quickshell
+import qs.config
+import qs.services
+import "../modules/osd"
+
+PanelWindow {
+    id: root
+
+    property bool shown: false
+
+    color: "transparent"
+    exclusionMode: ExclusionMode.Ignore
+    visible: shown
+    implicitWidth: card.implicitWidth
+    implicitHeight: card.implicitHeight
+
+    anchors.bottom: true
+    margins.bottom: screen.height * Theme.volume.bottomMarginRatio
+
+    // An empty click mask prevents the window from blocking mouse events.
+    mask: Region {}
+
+    Connections {
+        target: Audio
+
+        function onVolumeChanged() {
+            root.shown = true;
+            hideTimer.restart();
+        }
+
+        function onMutedChanged() {
+            root.shown = true;
+            hideTimer.restart();
+        }
+    }
+
+    Timer {
+        id: hideTimer
+
+        interval: Theme.volume.timeout
+        onTriggered: root.shown = false
+    }
+
+    VolumeCard {
+        id: card
+
+        anchors.fill: parent
+    }
+}