scaffold MkDocs Material handbook site

Initialize the public Rethink Studios docs site:
- mkdocs.yml: Material theme, light/dark palette toggle, pymdownx
  extensions, search, four-section nav skeleton.
- docs/index.md landing page with a card grid.
- Stub index pages for deploy, conventions, libraries, runbooks.
- .gitignore excludes .claude/, site/, and Python build cruft.

Deploy guide deferred; deploy section is a placeholder for now.

Signed-off-by: disqualifier <dev@disqualifier.me>

.gitignore

@@ -0,0 +1,11 @@
+# Claude project scaffold — never committed
+.claude/
+
+# MkDocs build output
+site/
+
+# Python
+__pycache__/
+*.py[cod]
+.venv/
+venv/