feat: publish About CQRE pages (EN+CS), add MkDocs site config, fix broken cross-links

- about-cqre.md / about-cqre-cs.md: placeholders filled; unverified facts kept as
  invisible CONFIRM(Tom) comments pending Tom's review (2026-09-20 deadline)
- mkdocs.yml: Material theme, docs_dir=antifragile-consulting, repo_url to Gitea
- Fix broken relative links in index, assessment-team-guide, engagement-checklist,
  engagement-model, rapid-modernisation-plan, assessment-templates/README
- Include previously untracked core/interdiction-model.md (Tom's WIP, appears complete)
- .gitignore: exclude site/ build output

mkdocs.yml

@@ -0,0 +1,51 @@
+site_name: Antifragile Enterprise — CQRE Brownhat
+site_description: Frameworks, playbooks and assessments for antifragile organizations. CQRE Brownhat consulting.
+site_url: https://antifragile.cqre.net/
+repo_url: https://git.cqre.net/cqrenet/antifragile
+docs_dir: antifragile-consulting
+
+# Root README.md duplicates index.md as a landing page; keep it out of the nav.
+exclude_docs: |
+  /README.md
+
+theme:
+  name: material
+  language: en
+  palette:
+    - scheme: default
+      primary: blue grey
+      accent: amber
+      toggle:
+        icon: material/brightness-7
+        name: Switch to dark mode
+    - scheme: slate
+      primary: blue grey
+      accent: amber
+      toggle:
+        icon: material/brightness-4
+        name: Switch to light mode
+  features:
+    - navigation.indexes
+    - navigation.sections
+    - navigation.top
+    - navigation.footer
+    - search.highlight
+    - content.action.view
+
+plugins:
+  - search
+
+markdown_extensions:
+  - admonition
+  - attr_list
+  - md_in_html
+  - tables
+  - toc:
+      permalink: true
+  - pymdownx.details
+  - pymdownx.superfences
+  - pymdownx.highlight:
+      anchor_linenums: true
+
+extra:
+  generator: false