chore: enable Mermaid diagrams via material theme config

Author: shenxianpeng

docs/projects.md

@@ -9,37 +9,30 @@ The commit-check ecosystem is built on a simple architecture: **one policy engin
 multiple enforcement surfaces.** Write your `cchk.toml` once — every surface
 reads the same file.
 
-<div class="grid cards" markdown>
-
--   :material-file-document-outline: **One policy: `cchk.toml`**
-
-    ---
-
-    Write your rules once, enforce everywhere.
-
-    ↓
-
--   :fontawesome-brands-python: **commit-check** (core engine)
-
-    ---
-
-    CLI · pre-commit · Python API
-
-    ↓
-
--   :material-github: **commit-check-action**
-
-    ---
-
-    GitHub Action → CI Pipeline
-
--   :material-robot: **commit-check-mcp**
-
-    ---
-
-    MCP Server → AI Coding Agent
-
-</div>
+```mermaid
+graph TB
+    subgraph Policy["📄 cchk.toml"]
+        direction LR
+        Config[One policy file]
+    end
+
+    subgraph Engine["⚙️ commit-check<br/>(Python core)"]
+        direction LR
+        CLI[CLI & pre-commit]
+        API[Python API]
+    end
+
+    subgraph Surfaces["🚀 Enforcement surfaces"]
+        Action[commit-check-action<br/>GitHub Action]
+        MCP[commit-check-mcp<br/>MCP Server]
+    end
+
+    Config --> Engine
+    CLI --> Action
+    API --> MCP
+    Action --> CI[CI Pipeline]
+    MCP --> Agent[AI Coding Agent]
+```
 
 | Surface | What it does | Get started |
 |---------|-------------|-------------|

mkdocs.yml

@@ -56,7 +56,11 @@ theme:
 
 
 markdown_extensions:
-  - pymdownx.superfences
+  - pymdownx.superfences:
+      custom_fences:
+        - name: mermaid
+          class: mermaid
+          format: !!python/name:pymdownx.superfences.fence_code_format
   - attr_list
   - md_in_html
   - pymdownx.tabbed: