Align panel underlines with native bar icons

shell/plugins/bar/Bar.qml

@@ -1886,11 +1886,12 @@ Item {
       // desktop — so it underlines a top bar, overlines a bottom one, and
       // points inward from a left or right one. It reads as pointing at the
       // panel that opens on that side.
+      // Snap toward the start of the slot, matching native glyph rendering.
       x: root.vertical
         ? (root.position === "left" ? parent.width - width - inset : inset)
-        : Math.round((parent.width - width) / 2)
+        : Math.floor((parent.width - width) / 2)
       y: root.vertical
-        ? Math.round((parent.height - height) / 2)
+        ? Math.floor((parent.height - height) / 2)
         : (root.position === "top" ? parent.height - height - inset : inset)
       z: 50