fix(bar): exclude niri from fullscreen toplevel detection (#2091)

Niri already renders fullscreen windows above the top layer-shell layer
(see render_above_top_layer() in niri's scrolling.rs). Aside from
redundancy, this check also hides the bar for windowed-fullscreen
windows (aka fake fullscreen), since the Wayland protocol reports
identical state for both.

quickshell/Modules/DankBar/DankBarWindow.qml

@@ -181,7 +181,7 @@ PanelWindow {
     }
 
     function _updateHasFullscreenToplevel() {
-        if (!CompositorService.isHyprland && !CompositorService.isNiri) {
+        if (!CompositorService.isHyprland) {
             hasFullscreenToplevel = false;
             return;
         }