feat: add IPC handler for toggling window fullscreen state

Helpers/IPCHandlers.qml

@@ -1,4 +1,5 @@
 import Quickshell.Io
+import Quickshell.Wayland
 
 IpcHandler {
     property var appLauncherPanel
@@ -6,6 +7,22 @@ IpcHandler {
 
     target: "globalIPC"
 
+    // Toggle Fullscreen
+    function toggleFullscreen(): void {
+        console.log("[IPC] toggleFullscreen() called")
+        if (ToplevelManager.activeToplevel) {
+            if (ToplevelManager.activeToplevel.fullscreen) {
+                // Exit fullscreen
+                ToplevelManager.activeToplevel.fullscreen = false;
+            } else {
+                // Enter fullscreen
+                ToplevelManager.activeToplevel.fullscreen = true;
+            }
+        } else {
+            console.warn("[IPC] No active toplevel window to toggle fullscreen");
+        }
+    }
+
     // Toggle Applauncher visibility
     function toggleLauncher(): void {
         if (!appLauncherPanel) {