Add Noctalia shell with Quickshell overview

- Add `noctalia` input to flake and lock it in `flake.lock`.
- Include `noctalia` and `quickshell` modules in `flake.nix`.
- Extend core packages to accept `inputs` and `system`; add
  `quickshell.nix`
  with required Qt6 packages and environment variables.
- Enable `upower` service for battery handling.
- Add home modules `noctalia.nix` and `overview.nix` (QML UI, README,
  assets, widgets, services) to provide a workspace overview.
- Comment out unused rofi and web‑search binds; update `exec‑once` to
  start
  the overview daemon and `noctalia-shell`.
- Provide `restart.noctalia` script and its Nix wrapper.
- Enable `noctalia-shell` in `stylix` configuration.

modules/home/overview/common/widgets/StyledRectangularShadow.qml

@@ -0,0 +1,14 @@
+import QtQuick
+import QtQuick.Effects
+import ".."
+
+RectangularShadow {
+    required property var target
+    anchors.fill: target
+    radius: 20
+    blur: 0.9 * Appearance.sizes.elevationMargin
+    offset: Qt.vector2d(0.0, 1.0)
+    spread: 1
+    color: Appearance.colors.colShadow
+    cached: true
+}