Although it is hard to see in the graphic, it looks like you have the lines added in the incorrect place....that is, getting the { } unbalanced. "edit: Actually, looking again, that might not be the case, but you might want to try the below anyway.
I put the added lines at the top, right after the ... "widgets": [
I think you have yours pasted in the brackets right under the version line.
I'll attached a copy of my the <WAB>\client\stemapp\predefined-apps\default\config.json mine. They should be generic, but I would rename/move yours, put mine in it's place (rename the .txt back to .json) and make sure the NodeJS and WAB are totally closed.
A reboot would not hurt. For some reason, fixing or trying to add the LocalLayer even to a 2.5 app I created earlier did not work....for a few hours. a bit puzzling but my guess is NodeJS was not fully shut down.
Also in my doc, I had written that sometimes you need to edit the app, save, shutdown/reboot and try it again...if it doesn't work with the first shutdown/reboot.
edit2: ...oops, see you just got it working.