Only set initial MenuItem focus if not activating via mouse

Having an initially highlighted item when using mouse navigation
doesn't adhere to UX norms and also can lead to a janky feeling
when the focus flip-flops from the item under the user's cursor
to the first item as the Menu opens.

app/gui/PcView.qml

@@ -165,6 +165,7 @@ CenteredGridView {
             asynchronous: true
             sourceComponent: NavigableMenu {
                 id: pcContextMenu
+                initiator: pcContextMenuLoader.parent
                 MenuItem {
                     text: qsTr("PC Status: %1").arg(model.online ? qsTr("Online") : qsTr("Offline"))
                     font.bold: true