I have looked at this a little and I may be able to help. I am not sure how much time I will have in the immediate future because there are some potentially major bugs in Bob that I need to take care of in addition to my day job but this looks like a good project.
I think that using the way that the sjcl encryption library is included is a good start. The minified sjcl.js file as part of the core plugin along with a .meta file for it. I think that copying that is the way to go. I am not exactly sure how the library is loaded, that may be enough.
The library is used in the crypto function in boot.js here
https://github.com/Jermolene/TiddlyWiki5/blob/929b0c98330ad25aa4a32cd201274a6e89cd8902/boot/boot.js#L601Looking at that it has different methods of loading depending on platform, on node it uses require like you suggested, but that isn't available in the browser but the library is available as window.sjcl. I assume this is done when the sjcl.js library is loaded, either by tiddlywiki or the library itself, but I am not certain.
I hope that is enough to get started because I have to run for a bit.