kf5: replace sloppy focus with click-to-focus

The hover-based sloppy focus timer was stealing focus from buttons
via paneRoot.focus=true every 100ms of mouse movement, making
buttons very hard to click.

Replace with a click-to-focus MouseArea that only updates the
focusedPaneIndex on actual clicks, with mouse.accepted=false
so clicks propagate to the target widget normally.

gui/main-kf5.qml

@@ -1385,21 +1385,13 @@ ApplicationWindow {
                 }
             }
 
-            // Sloppy focus
+            // Click-to-focus: update focused pane index on click
             MouseArea {
                 anchors.fill: parent
-                hoverEnabled: true
-                acceptedButtons: Qt.NoButton
+                acceptedButtons: Qt.LeftButton
                 propagateComposedEvents: true
-                onPositionChanged: sloppyTimer.restart()
-                onExited: sloppyTimer.stop()
-            }
-            Timer {
-                id: sloppyTimer
-                interval: 100
-                onTriggered: {
-                    paneRoot.focus = true
-                    // Update focused index
+                onPressed: {
+                    mouse.accepted = false
                     for (var i = 0; i < mainContent.panes.length; i++) {
                         if (mainContent.panes[i] === paneRoot) {
                             mainContent.focusedPaneIndex = i