Nothing fancy, just a few home grown shell scripts to essentially replace external dependencies in the html (e.g. script tags or link tags) with the contents of those files. There's no minifying, optimization, or building or anything. I only use vanilla js, css and html. The only exception to this is if I have anything that needs compiling to wasm, which essentially is just SQLite, but could be anything really.
Because I only deploy these locally on desktops it's pretty much pointless to build/obfuscate/optimize anything for transport, it's so fast to load anyway since it's all off the local drive.
Maybe I should write up a how-to or tidy up the workflow and publish, but it's really nothing fancy.