Add Documentation link + screenshots to README and docs site

theta-env's GitHub Pages site (docs/, Jekyll) was already configured and
live at https://theta42.github.io/theta-env/ but nothing in the README
linked to it, unlike proxy and sso-manager-node's READMEs -- easy to miss
entirely. Add the same top-of-README Documentation link, plus screenshots
of the composed stack (SSO dashboard + proxy host list from one
./setup.sh run). Also fixes a stale docs/index.md quickstart snippet that
said "set CFG_BASE_DN to your domain" -- CFG_DOMAIN is the actual
required variable (CFG_BASE_DN is an advanced override); everywhere else
in the docs already says CFG_DOMAIN correctly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -16,6 +16,16 @@ Each project still runs **standalone** (`docker compose up` in its own folder);
 this repo just composes them and automates the first-run glue so they find each
 other.
 
+**Documentation:** [https://theta42.github.io/theta-env/](https://theta42.github.io/theta-env/)
+
+## Screenshots
+
+The SSO Manager and the proxy it fronts, both stood up by one `./setup.sh` run:
+
+| SSO Manager Dashboard | Proxy Hosts |
+| --- | --- |
+| ![SSO Manager dashboard](docs/images/sso-dashboard.png) | ![Proxy host list](docs/images/proxy-hosts.png) |
+
 **Why use this instead of running the two separately?** The two only become
 useful once the proxy is registered as an OIDC client of the SSO and pointed at
 the SSO's LDAP directory — and the SSO's domain has to match across half a dozen