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>

docs/index.md

@@ -0,0 +1,46 @@
+# Rethink Studios Handbook
+
+The shared reference for how we build, deploy, and operate. Generic patterns and
+conventions live here — sanitized for public consumption. Real infrastructure
+specifics (hostnames, internal IPs, secrets, exact topology) stay in our private
+runbooks.
+
+## Sections
+
+<div class="grid cards" markdown>
+
+-   :material-rocket-launch: __[Deploy](deploy/index.md)__
+
+    ---
+
+    How services get from a repo to running behind the proxy — container
+    standards, compose patterns, and step-by-step deploy guides.
+
+-   :material-ruler-square: __[Conventions](conventions/index.md)__
+
+    ---
+
+    Coding, library, and infrastructure conventions. Naming, layout, logging,
+    and the rules that keep things consistent across projects.
+
+-   :material-package-variant: __[Libraries](libraries/index.md)__
+
+    ---
+
+    Usage docs for the shared `rethink-public` library suite — what each lib
+    does and how to wire it into a project.
+
+-   :material-tools: __[Runbooks](runbooks/index.md)__
+
+    ---
+
+    Operational how-tos for recurring tasks — sanitized for public reference.
+
+</div>
+
+## Conventions for this handbook
+
+- One topic per page, grouped by section directory.
+- Public means sanitized: use placeholders (`<host>`, `<dev>`, `/srv/...`) and
+  describe the pattern, not our literal infrastructure.
+- Code blocks are tagged with their language and kept copy-pasteable.