Prevent using an opaque surface for bar

The bar supports switching between transparent and opaque. That means we
can't use an opaque surface for it; if we did, it would be unable to
reliably render as transparent when needed.

This fixes a visual glitch where the background of a transparent bar
would flicker, particularly during mouse hover.

shell/plugins/bar/Bar.qml

@@ -819,6 +819,7 @@ Item {
     implicitWidth: root.vertical ? root.barSize : 0
     implicitHeight: root.vertical ? 0 : root.barSize
     color: root.transparent ? "transparent" : root.background
+    surfaceFormat.opaque: false
     WlrLayershell.namespace: "omarchy-bar"
     WlrLayershell.layer: WlrLayer.Top