Remove the pre-mike Sphinx directories from the gh-pages root

[LukasGold]

The gh-pages root still holds a complete copy of the Sphinx site that was
deployed before mike. Those paths return 200 and serve content frozen at
2026-07-07. They will never update.

URL	Serves
https://opensemanticlab.github.io/osw-python/tools/	the 2026-07-07 Sphinx page
https://opensemanticlab.github.io/osw-python/latest/tools/	the current page

A 200 on an unversioned path is therefore misleading. It looks like a working
documentation link and shows a superseded page.

Entries to remove

Unchanged since the last Sphinx deployment
641d919:

assets, auth, authors, changelog, conf.py, contributing,
controller, license, Makefile, model, objects.inv, osw, readme,
requirements.txt, search, tools, tutorials, 404.html

Entries to keep

• .nojekyll - its blob matches the July one only because the file is empty.
• Everything mike manages: index.html, versions.json, sitemap.xml,
  sitemap.xml.gz, dev, latest, and the version directories 2.0.0 to
  2.7.1.

Precondition

The repository no longer links to these paths after
7da804e. Do the removal
once that commit is on main, otherwise README.md links turn from stale
content into a 404.

Context

Deferred from #201, which
fixed the Pages setting so the site serves mike's current build again.

[LukasGold]

Correction on 404.html, found while reviewing this list.

GitHub Pages serves a custom 404 only from the root 404.html. The root
copy is the Sphinx one. mike and Zensical write a 404.html inside each
version directory (latest/404.html exists), but Pages ignores those.

So removing the root 404.html replaces the project's 404 page with GitHub's
default. GET /repos/OpenSemanticLab/osw-python/pages currently reports
"custom_404": true.

Two options, both acceptable:

• Keep the root 404.html and remove the other 17 entries.
• Replace the root 404.html with a copy of latest/404.html, so the 404 page
  matches the current theme. It needs its asset paths rewritten to latest/,
  otherwise its CSS and JS resolve against the root and 404 as well.