Fix pointer navigation in Quattro launcher menus (#6343)

Accumulate sub-threshold movement so slow motion with a flat acceleration profile updates selection. Sample pointer state on row entry and carry pointer intent through subordinate menus while preserving predictable keyboard selection.

shell/Ui/PointerMoveGate.qml

@@ -2,22 +2,31 @@ import QtQuick
 
 // Filters synthetic hover churn from moving delegates under a stationary
 // pointer. Call reset() after keyboard/list mutations, then moved() from a
-// row MouseArea's onPositionChanged before changing cursor selection.
+// row MouseArea's onPositionChanged before changing cursor selection. A
+// transition known to originate from the pointer can call allowInitialSample()
+// so the item under the stationary pointer remains selected.
 QtObject {
   id: root
 
   property Item referenceItem: null
   property real threshold: 1
   property bool primed: false
+  property bool initialSampleAllowed: false
   property real lastX: 0
   property real lastY: 0
 
   function reset() {
     root.primed = false
+    root.initialSampleAllowed = false
     root.lastX = 0
     root.lastY = 0
   }
 
+  function allowInitialSample() {
+    root.reset()
+    root.initialSampleAllowed = true
+  }
+
   function moved(item, mouse) {
     if (!item || !mouse) {
       root.reset()
@@ -26,12 +35,19 @@ QtObject {
 
     var target = root.referenceItem || item
     var point = item.mapToItem(target, mouse.x, mouse.y)
-    var didMove = root.primed
-      && (Math.abs(point.x - root.lastX) > root.threshold || Math.abs(point.y - root.lastY) > root.threshold)
+    var firstSample = !root.primed
+    var didMove = !firstSample
+      ? Math.abs(point.x - root.lastX) > root.threshold || Math.abs(point.y - root.lastY) > root.threshold
+      : root.initialSampleAllowed
 
-    root.lastX = point.x
-    root.lastY = point.y
+    // Keep the previous accepted position while filtering jitter so slow,
+    // sub-threshold steps accumulate into deliberate pointer movement.
+    if (firstSample || didMove) {
+      root.lastX = point.x
+      root.lastY = point.y
+    }
     root.primed = true
+    root.initialSampleAllowed = false
 
     return didMove
   }