restructure handbook to flat-page spec

Replace the four-section dir layout with the revised flat-page spec:
- Three-page nav: Libraries, Standards, Deploy.
- libraries.md: live client-side fetch of the rethink-public org from the
  Gitea API, denylist-filtered, sorted table linking each repo, no version
  pins, graceful fallback on fetch/CORS failure.
- standards.md: house coding standards.
- deploy.md: deploy guide for rethink-net (services uid 1337, uid-agnostic
  Docker, paths/mounts, bind-mount permissions, read-only secrets).
- index.md landing card grid updated for the three sections.
- gitignore Playwright MCP artifacts.

Verified: mkdocs build --strict clean; libraries fallback renders live.
Signed-off-by: disqualifier <dev@disqualifier.me>

mkdocs.yml

@@ -1,5 +1,5 @@
 site_name: Rethink Studios Handbook
-site_description: Deploy guides, infra and container standards, conventions, library usage, and runbooks.
+site_description: Libraries, coding standards, and how to deploy on our network.
 site_url: https://docs.rethinkstudios.io/
 copyright: Rethink Studios
 
@@ -24,9 +24,7 @@ theme:
   features:
     - navigation.instant
     - navigation.tracking
-    - navigation.sections
     - navigation.top
-    - navigation.indexes
     - toc.follow
     - search.suggest
     - search.highlight
@@ -59,11 +57,6 @@ plugins:
 
 nav:
   - Home: index.md
-  - Deploy:
-      - deploy/index.md
-  - Conventions:
-      - conventions/index.md
-  - Libraries:
-      - libraries/index.md
-  - Runbooks:
-      - runbooks/index.md
+  - Libraries: libraries.md
+  - Standards: standards.md
+  - Deploy: deploy.md