fix(ui): keep Space for playback after mouse clicks

Controls take focus only via Tab, so a click leaves Space for playback.

src/qml/VolumeSlider.qml

@@ -20,7 +20,7 @@ Slider {
     implicitWidth: Kirigami.Units.gridUnit * 5
     wheelEnabled: true
     stepSize: QtPotatoSettings.volumeStep
-    focusPolicy: Qt.StrongFocus
+    focusPolicy: Qt.TabFocus
 
     // Let the Slider consume navigation keys before window playback shortcuts.
     Keys.onShortcutOverride: event => {