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>

mkdocs.yml

@@ -0,0 +1,69 @@
+site_name: Rethink Studios Handbook
+site_description: Deploy guides, infra and container standards, conventions, library usage, and runbooks.
+site_url: https://docs.rethinkstudios.io/
+copyright: Rethink Studios
+
+theme:
+  name: material
+  language: en
+  palette:
+    - media: "(prefers-color-scheme: light)"
+      scheme: default
+      primary: indigo
+      accent: indigo
+      toggle:
+        icon: material/weather-night
+        name: Switch to dark mode
+    - media: "(prefers-color-scheme: dark)"
+      scheme: slate
+      primary: indigo
+      accent: indigo
+      toggle:
+        icon: material/weather-sunny
+        name: Switch to light mode
+  features:
+    - navigation.instant
+    - navigation.tracking
+    - navigation.sections
+    - navigation.top
+    - navigation.indexes
+    - toc.follow
+    - search.suggest
+    - search.highlight
+    - content.code.copy
+    - content.code.annotate
+  icon:
+    repo: fontawesome/brands/git-alt
+
+markdown_extensions:
+  - admonition
+  - attr_list
+  - md_in_html
+  - tables
+  - toc:
+      permalink: true
+  - pymdownx.details
+  - pymdownx.superfences
+  - pymdownx.tabbed:
+      alternate_style: true
+  - pymdownx.highlight:
+      anchor_linenums: true
+  - pymdownx.inlinehilite
+  - pymdownx.snippets
+  - pymdownx.emoji:
+      emoji_index: !!python/name:material.extensions.emoji.twemoji
+      emoji_generator: !!python/name:material.extensions.emoji.to_svg
+
+plugins:
+  - search
+
+nav:
+  - Home: index.md
+  - Deploy:
+      - deploy/index.md
+  - Conventions:
+      - conventions/index.md
+  - Libraries:
+      - libraries/index.md
+  - Runbooks:
+      - runbooks/index.md