feat(quickshell): idle chain, drifting wallpaper, and a few fixes

- Idle is handled in the shell instead of hypridle: the screen dims
  slowly at 4 minutes, locks at 5, powers down at 6, and suspends at 15
  on battery. Idle inhibitors hold every stage off; Super+Shift+I does
  the same by hand and puts a cup on the rail.
- The shell draws the wallpaper (backdrop/), so hyprpaper is gone. The
  picture is drawn a little larger than the screen and drifts with the
  workspace a beat after the windows, and dims a shade while windows are
  open. The path lives in quickshell/wallpaper.
- The lock screen and power menu say "Take your time." instead of the
  NieR slogan.
- hyprpaper is no longer launched twice, the media module keeps the
  player that played last instead of an empty browser tab, and grouped
  windows show thin untitled tabs with their place in the group (2/3)
  in the bar title.
- qt6ct uses Darkly; the package list gains adw-gtk-theme and darkly-bin.

quickshell/backdrop/Backdrop.qml

@@ -0,0 +1,90 @@
+import QtQuick
+import Quickshell
+import Quickshell.Hyprland
+import Quickshell.Wayland
+import "root:/config"
+import "root:/services"
+
+// The wallpaper, seen through the porthole. It is drawn a little larger than
+// the screen and drifts when the workspace changes: windows slide past
+// vertically (hypr/lua/animations.lua) and the scene behind them moves a few
+// pixels the same way and a little later, the way distant things do out of a
+// moving window. Only on switches — it never moves on its own, so an idle
+// desktop costs the compositor nothing.
+//
+// It also settles a shade darker while the workspace holds windows, so the
+// band of wallpaper round them reads as the far side of the glass rather than
+// as part of the desktop.
+PanelWindow {
+    id: root
+
+    required property var modelData
+    screen: modelData
+
+    WlrLayershell.layer: WlrLayer.Background
+    WlrLayershell.namespace: "takemi-backdrop"
+    WlrLayershell.keyboardFocus: WlrKeyboardFocus.None
+    exclusionMode: ExclusionMode.Ignore
+    anchors { top: true; bottom: true; left: true; right: true }
+    color: Theme.ink
+    mask: Region {}
+
+    readonly property HyprlandMonitor monitor: Hyprland.monitorFor(root.screen)
+    readonly property HyprlandWorkspace workspace: root.monitor?.activeWorkspace ?? null
+
+    // Overscan: how much bigger than the screen the picture is drawn, which is
+    // the room it has to drift in.
+    readonly property real overscan: 1.08
+    readonly property real slack: root.height * (root.overscan - 1)
+
+    // Workspaces 1–10 spread across the slack, so 1 sits at the top of the
+    // picture and each step down moves it a fixed distance. Special and
+    // named workspaces (negative ids) leave it where it was.
+    property real drift: 0
+    readonly property int wsId: root.workspace?.id ?? 1
+    onWsIdChanged: if (root.wsId > 0) root.drift = Math.min(root.wsId - 1, 9) / 9
+
+    readonly property bool occupied: (root.workspace?.toplevels?.values?.length ?? 0) > 0
+
+    Image {
+        id: picture
+        width: root.width * root.overscan
+        height: root.height * root.overscan
+        x: -(width - root.width) / 2
+        y: -root.drift * root.slack
+        source: Wallpaper.forMonitor(root.screen?.name ?? "")
+        sourceSize: Qt.size(width, height)
+        fillMode: Image.PreserveAspectCrop
+        asynchronous: true
+        smooth: true
+        cache: false
+
+        opacity: status === Image.Ready ? 1 : 0
+
+        Behavior on opacity {
+            NumberAnimation { duration: Theme.durLazy; easing.type: Easing.OutCubic }
+        }
+
+        // Longer than Hyprland's 550ms workspace slide, on the same curve, so
+        // the windows arrive first and the scene catches up.
+        Behavior on y {
+            NumberAnimation {
+                duration: 900
+                easing.type: Easing.BezierSpline
+                easing.bezierCurve: [0.35, 0.0, 0.15, 1.0, 1.0, 1.0]
+            }
+        }
+    }
+
+    Rectangle {
+        anchors.fill: parent
+        color: Theme.ink
+        opacity: root.occupied ? 0.18 : 0
+
+        Behavior on opacity {
+            NumberAnimation { duration: Theme.durLazy; easing.type: Easing.InOutSine }
+        }
+    }
+
+    Component.onCompleted: root.drift = Math.min(Math.max(root.wsId, 1) - 1, 9) / 9
+}