First off - thank you for all your help! I greatly appreciate how quickly you've been responding. I finally had a moment to take a crack at this tonight, and figured I'd report back.
I went ahead and grabbed nwjs and used the terminal command you provided me! I had to tweak the file path just a little to make sure it aligned with the folder names, as a straight copy/paste didn't accomplish anything. I went ahead and tried a file path for both the layers of folders alongside the app for the sake of completeness. Didn't want to accidentally mess things up, as I'm not sure what I'm doing.
The end result of this was the same error being thrown by nwjs every attempt - "Manifest file missing or unreadable." I'm hoping that's a clue for your bug hunt, and not an indication of me mangling the command somehow!