docs: MkDocs site with flow diagrams; RustFS permissions

Material for MkDocs site (mkdocs.yml, optional extra `docs`) with Mermaid via
the superfences custom fence. New pages: overview, scanning (modes, quick
rules, Joern engine, priors, pre-push delta), the plane on ax (one task as a
sequence, golden snapshot, Run DAGs), memory (row kinds, write/read paths,
FileStore vs S3, verify at startup), memory and detection, and RustFS setup
(admin steps, complete agent policy, .env, refusal messages, Select limit).
The ops READMEs are included at build time; evaluation gains the population
lifecycle and the fold layout. tests/test_docs_site.py runs the strict build
when mkdocs is importable and checks Mermaid blocks and the RustFS page.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

mkdocs.yml

@@ -0,0 +1,66 @@
+site_name: OpenUltraSAST
+site_description: An experimental static security analyser and repository safety net, with an agentic plane and a learned decision engine in development.
+repo_url: https://github.com/norandom/OpenUltraSAST
+edit_uri: edit/main/docs/
+docs_dir: docs
+site_dir: site
+strict: true
+
+theme:
+  name: material
+  features:
+    - navigation.sections
+    - navigation.top
+    - content.code.copy
+    - search.highlight
+  palette:
+    - media: "(prefers-color-scheme: light)"
+      scheme: default
+      toggle:
+        icon: material/brightness-4
+        name: Dark mode
+    - media: "(prefers-color-scheme: dark)"
+      scheme: slate
+      toggle:
+        icon: material/brightness-7
+        name: Light mode
+
+validation:
+  omitted_files: warn
+  absolute_links: warn
+  unrecognized_links: warn
+  anchors: warn
+
+markdown_extensions:
+  - admonition
+  - attr_list
+  - tables
+  - toc:
+      permalink: true
+  - pymdownx.details
+  - pymdownx.snippets:
+      base_path: ["."]
+      check_paths: true
+  - pymdownx.superfences:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:pymdownx.superfences.fence_code_format
+
+nav:
+  - Overview: index.md
+  - How it works:
+      - Scanning: scanning.md
+      - Architecture: architecture.md
+      - The plane on ax: plane.md
+      - Memory: memory.md
+      - Memory and detection: memory-and-detection.md
+      - Decision engine: decision-engine.md
+  - Evaluation: evaluation.md
+  - Using it:
+      - Examples: examples.md
+      - Threat model: threat-model.md
+  - Operations (maintainers):
+      - Engine and pre-push: ops/README.md
+      - ax on this host: ops/ax/README.md
+      - RustFS setup for the memory store: rustfs.md