feat: add Mermaid diagram support to docsite

Install @docusaurus/theme-mermaid and enable markdown.mermaid
so flowcharts and diagrams render as SVG instead of raw text.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: gHashTag

docsite/docusaurus.config.ts

@@ -39,7 +39,11 @@ const config: Config = {
     },
   ],
 
-  themes: ['@docusaurus/theme-live-codeblock'],
+  markdown: {
+    mermaid: true,
+  },
+
+  themes: ['@docusaurus/theme-live-codeblock', '@docusaurus/theme-mermaid'],
 
   presets: [
     [