refactor -> class jsbundle

[milahu]

reduce the nunjuck interface to

{% jsBundleHead %}{# vite js bundle #}
...
{% jsBundleFoot %}{# vite js bundle #}

reduce the config interface to

new JsBundle(staticConfig).addNunjucksShortcodes(eleventyConfig);

factor out the staticConfig part of .eleventy.js

read manifest.json only once

remove unneeded async code

prettify output of concurrently

use cross-env and npm-run-all for cross platform

set vite devserver port with https://github.com/imwtr/find-free-port-sync

move most config to .eleventy.js

use sirv-cli as http server - lightweight

dependencies: use latest versions by default

todo: ignore src/client (etc.) via .eleventy.js not .eleventyignore (centralize config)
-> wontfix @ https://github.com/11ty/eleventy/issues/188