chore: replace mermaid chart with markdown cards for compatibility

Author: shenxianpeng

docs/projects.md

@@ -9,30 +9,37 @@ 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.
 
-```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]
-```
+<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>
 
 | Surface | What it does | Get started |
 |---------|-------------|-------------|