overview backdrop: test pattern, niri layer-rule in hm-module

modules/OverviewBackdrop.qml

@@ -0,0 +1,78 @@
+import QtQuick
+import Quickshell
+import Quickshell.Wayland
+import "." as M
+
+// Rendered in niri's overview backdrop via place-within-backdrop layer rule.
+// Visible between workspace rows during overview.
+PanelWindow {
+    id: root
+
+    required property var screen
+
+    color: "transparent"
+
+    WlrLayershell.layer: WlrLayer.Background
+    WlrLayershell.exclusiveZone: -1
+    WlrLayershell.namespace: "nova-overview-backdrop"
+    mask: Region {}
+
+    anchors.top: true
+    anchors.left: true
+    anchors.right: true
+    anchors.bottom: true
+
+    // Test pattern — diagonal gradient with centered label
+    Rectangle {
+        anchors.fill: parent
+        gradient: Gradient {
+            orientation: Gradient.Horizontal
+            GradientStop {
+                position: 0
+                color: Qt.rgba(M.Theme.base0C.r, M.Theme.base0C.g, M.Theme.base0C.b, 0.15)
+            }
+            GradientStop {
+                position: 0.5
+                color: Qt.rgba(M.Theme.base0E.r, M.Theme.base0E.g, M.Theme.base0E.b, 0.1)
+            }
+            GradientStop {
+                position: 1
+                color: Qt.rgba(M.Theme.base09.r, M.Theme.base09.g, M.Theme.base09.b, 0.15)
+            }
+        }
+    }
+
+    // Grid of dots as a test pattern
+    Grid {
+        anchors.fill: parent
+        columns: Math.floor(width / 80)
+        rows: Math.floor(height / 80)
+
+        Repeater {
+            model: parent.columns * parent.rows
+            Rectangle {
+                width: 80
+                height: 80
+                color: "transparent"
+                Rectangle {
+                    anchors.centerIn: parent
+                    width: 4
+                    height: 4
+                    radius: 2
+                    color: M.Theme.base0D
+                    opacity: 0.2
+                }
+            }
+        }
+    }
+
+    Text {
+        anchors.centerIn: parent
+        text: "nova-shell overview backdrop"
+        color: M.Theme.base05
+        opacity: 0.3
+        font.pixelSize: 24
+        font.family: M.Theme.fontFamily
+        font.letterSpacing: 6
+    }
+}

modules/qmldir

@@ -34,3 +34,4 @@ Notifications 1.0 Notifications.qml
 Power 1.0 Power.qml
 Privacy 1.0 Privacy.qml
 BackgroundOverlay 1.0 BackgroundOverlay.qml
+OverviewBackdrop 1.0 OverviewBackdrop.qml