fix(macOS): detach menu when no items are present

Ensured the native menu is cleared (`null`) on macOS when no menu items are available, allowing the system to detach the menu properly.

Author: kdroidFilter

src/commonMain/kotlin/com/kdroid/composetray/lib/mac/MacTrayManager.kt

@@ -203,6 +203,8 @@ internal class MacTrayManager(
         val trayObj = tray ?: return
 
         if (menuItems.isEmpty()) {
+            // When there are no menu items, clear the native menu pointer so macOS detaches the menu.
+            trayObj.menu = null
             return
         }