Shrink to a floating button instead of hiding

With "Shrink to Button" on, the dismiss key shrinks the window to just
itself: a see-through button that can be dragged anywhere. Tapping it
grows the keyboard back around it, kept on screen. KWin moves and
resizes the window through a one-off script, as Wayland clients can't
place themselves.

Also moves the window back on screen whenever it appears (KWin remembers
where the button was), and releases the mouse after a window manager
move or resize, which used to eat the next press on the grab bar.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

qml/SettingsPanel.qml

@@ -63,6 +63,14 @@ Flickable {
                     onToggled: checked => panel.settings.alwaysVisible = checked
                 }
 
+                ToggleRow {
+                    width: parent.width
+                    text: qsTr("Shrink to Button")
+                    detail: qsTr("⌨ leaves a floating button instead of hiding; tap it to bring the keyboard back")
+                    checked: panel.settings.collapseToButton
+                    onToggled: checked => panel.settings.collapseToButton = checked
+                }
+
                 ToggleRow {
                     width: parent.width
                     text: qsTr("“.” Shortcut")