put shell in subdir, and add nix package

shell/widgets/RoundSlider.qml

@@ -0,0 +1,55 @@
+pragma ComponentBehavior: Bound
+
+import QtQuick
+import QtQuick.Controls
+import Qt5Compat.GraphicalEffects
+import ".."
+
+Slider {
+    id: slider
+    implicitHeight: 8
+    property var accentColor: ShellSettings.colors["primary"]
+
+    background: Rectangle {
+        id: sliderContainer
+        width: slider.availableWidth
+        height: slider.implicitHeight
+        color: ShellSettings.colors["inverse_surface"]
+        radius: 4
+        anchors.verticalCenter: parent.verticalCenter
+
+        layer.enabled: true
+        layer.effect: OpacityMask {
+            source: Rectangle {
+                width: sliderContainer.width
+                height: sliderContainer.height
+                radius: sliderContainer.radius
+                color: "white"
+            }
+
+            maskSource: Rectangle {
+                width: sliderContainer.width
+                height: sliderContainer.height
+                radius: sliderContainer.radius
+                color: "black"
+            }
+        }
+
+        Rectangle {
+            id: fill
+            width: slider.handle.width / 2 + slider.visualPosition * (sliderContainer.width - slider.handle.width)
+            height: sliderContainer.height
+            color: Qt.color(slider.accentColor ?? "purple").darker(1.2)
+        }
+    }
+
+    handle: Rectangle {
+        id: handleRect
+        x: slider.visualPosition * (slider.availableWidth - width)
+        y: slider.topPadding + slider.availableHeight / 2 - height / 2
+        width: 16
+        height: 16
+        radius: width / 2
+        color: slider.pressed ? Qt.color(slider.accentColor ?? "purple").darker(1.5) : slider.accentColor ?? "purple"
+    }
+}