Simplify/Clarify Web site building

I think this use case deserves to be better explained, maybe in the "quickstart" section. Currently there are many things that are not very clear:

• An executable with (js_of_ocaml (..)) and a public name will build/install the .exe, not the .js. This is not intuitive.
• If I have an HTML file that uses the generated js, it's not clear how to put the website together in order to visit it without either pointing inside _build or moving the files around.
• What's the right way to handle static data and/or bundle additional js files?

I feel like the basic supports is there (and I ended up successfully building my .bc.js) but it feel fairly unfinished. I'm not sure what the idiomatic dune way is, but a little bit of polish would be sufficient to make the situation much better. Maybe with a new target that would put the files together and launch the website, or something like that ?

Start with the quickstart section and the existing js_of_ocaml build guidance; no specific files or tests are named in the issue. Reproduce the documented website-building flow, including generated JavaScript, HTML, static data, and additional JavaScript, then define the documentation or target behavior needed for a complete, clear workflow.