docs: static documentation site generator and authored pages

Twenty-six pages covering concepts, architecture, every subsystem, an
interface tour with screenshots, the full API route table generated from
openapi.json, the CLI, security and threat model, operations, ADRs,
development history and a glossary. Built into the dixon.cx page skeleton,
unlinked and noindex.

docs/site/README.md

@@ -0,0 +1,15 @@
+# Documentation site
+
+`build.py` renders the documentation section from the repository's Markdown,
+the OpenAPI document and the screenshots into static HTML that follows the
+dixon.cx page skeleton. Authored pages live in `pages/`; a page pulls a
+repository document in with `{{include path [demote=N] [keep-title]}}` and the
+API page uses `{{openapi}}`.
+
+```
+python3 -m venv .venv && .venv/bin/pip install markdown
+.venv/bin/python docs/site/build.py /path/to/public_html/noema
+```
+
+The output is intentionally not linked from the site navigation and carries a
+`noindex` robots directive.