Support HTML export as a readable/writable file format
The HTML export (specifically the .js file) is an interpretation of the binary version of a cart. It should be possible to support reading and writing exported .js files just like .p8 and .p8.png files.

With a bit more effort to store a version of the HTML file (released as open source by Lexaloffle), picotool should be able to fully "export" carts to HTML as part of a build workflow.