Docs: correct the claims, fix the rendering, add a Protocol section - #1

mkdocs.yml declared no markdown_extensions at all, so every fenced block on a
site made almost entirely of shell and Python rendered as bare <pre><code> -
no highlighting, and nothing for content.code.copy to attach a button to.

theme.features listed "navigation.instance", which mkdocs-material does not
have, so it was silently ignored. Correcting it to navigation.instant turns out
to break the build: mkdocs-static-i18n cannot keep the language switcher
contextual with instant loading on, and --strict fails. The typo was
accidentally load-bearing. Left out, with a comment saying why.

Also adds site_description, repo_url and edit_uri, so pages get an
"Edit this page" link.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

deploy-pages.yml only runs on a push to main, so a pull request got no
validation at all and a broken build was first visible after merging.
--strict makes a warning - a dead link, a page missing from the nav - fail
the check rather than ship.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

The boundary between the training server and the env client is the reason
this project exists, and the site never described it. A reader could learn
how to add an environment or a policy, but not what the two processes say
to each other, or that an env client need not be Python.

The page orients rather than duplicates: SPEC.md stays in plugrl-protocol,
next to the code it describes, so the two cannot drift. What is here is the
exchange diagram, the three rules a first implementation usually gets wrong
- strict alternation, feedback env sets that need not match the infer's,
and chunk-summed reward - the conformance server, and the relationship to
openpi.

Both languages. mkdocs build --strict passes; nav translations go from 10
elements to 11.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

It had no installation section at all. It opened with `plugrl-run-server`,
which requires two packages that are not on PyPI and that the page never
mentioned cloning. A reader arriving from the front page had nowhere to go.

It now begins with the clone-and-uv-sync for both repositories, then the FPO
quickstart that actually learns, then the dummy connectivity check labelled
as what it is.

It also names the two flags that are not optional and previously were not
mentioned anywhere: --policy.device cpu, because the default is cuda and the
server dies on startup without a GPU, and --algo.buffer-size, because at the
default a short run learns once at the very end.

The troubleshooting section now covers what a new user actually hits,
including both of those.

The Ray launcher is qualified here and in the user guide rather than listed
as an equal alternative to plugrl-run-server.

Both languages. mkdocs build --strict passes.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>