It's not hard, just tedious. I am also not sure if this falls under "cracked". Basically there are multiple options (in this case, Electron) that allow you to create an application that is basically just a web browser that can run local files. Once you play through the online version of the game, all of the files are in your browser cache. So basically you extract your browser cache into the proper folder, modify a couple of files that point you to the proper html file that launches the game for that chapter and you have a working offline version.
The tedious part is that, while it normally loads all the graphics into browser cache as long as you run the game and go through each path, it does not always download the sound files unless you go click-by-click. If you try to use the skip button to speed up the process, you will miss a lot of the .ogg files that play. The offline version will still run fine without those, but you will be missing some sound effects or music. Also, you HAVE to play through each path. If any of the graphic files are missing, the game will just show the "Downloading Assets" screen for good.
I just pulled down the versions I ported a while back and realized that I could probably make this into 1 file with a Table of Contents/Chapter List feature in the menu that would let you load any chapter without closing/re-opening the "app". I might play with that to see if that resolves the issue of having to manually backup/restore across chapters.