Modernize build environment for `airflow-site`

[potiuk]

Currently we use github action and "site" script to build airflow-site docs. But those tools there like npm and hugo are old and outdated and they do not run on modern OS-ses (MacOS ubuntu) - not out-of-the-box at leas.

We need to modernize the tooling and possibly have a dockerized environment to run them on on all kind of os's variants

Possibly we could also use go-hugo or Pelican

And we should have an easy way to run and test changes by contributors.

[potiuk]

Also we need a better description on how to test the layout changes with airflow-site - this is now a very small repo and apparently (as dicussed with @mik-laj - there is a "demo" part that should allow us to iterate quickly on site layout change) - so that would be great if we can improve it all and modernize (and describe how to do it for contributors like @simi - who could improve our documentation layout (see #52016 for example).

CC: @mik-laj -> if you could help with that (as discussed recently) - that would be super-awesome and we could finally close this huge task of modernizing our doc build environment !

[simi]

The best exeprience was using uv run devel-common/src/docs/build_docs.py apache-airflow --autobuild, but it sadly doesn't rebuild on this custom.css change. 😅

[potiuk]

Bonus points -> if we could make it AI-agent friendly i.e. have AGENTS.md description and easily replicable "build and test" environment, that would help people to vibe-code some changes. UI / Website/ Javascript changes are SUPER easy for AI tools to do properly (there are billions of example they learned from in the web) - so if our environment has quick and replicable build and test environment, we could literally vibe-code any changes - even by non-javascript experts.

[potiuk]

The best exeprience was using uv run devel-common/src/docs/build_docs.py apache-airflow --autobuild, but it sadly doesn't rebuild on this custom.css change. 😅

Yeah. That would be ideal, but it is different repo (airflow-site) and it pulls the theme from that repo. So I am not even sure if this change will work (@mik-laj ?)

BTW. You also have:

cd airflow-core
uv run build-docs --autobuild

That Also nicely works and builds documentation auto detecting which directory it is run from.