feat: Mark setup as completed when user clicks Done button (#529)

Closes #523

Author: msanatan

MCPForUnity/Editor/Windows/MCPSetupWindow.cs

@@ -97,6 +97,7 @@ private void OnRefreshClicked()
 
         private void OnDoneClicked()
         {
+            Setup.SetupWindowService.MarkSetupCompleted();
             Close();
         }