fix: add pentest architecture to sidebar, fix image paths, enable mermaid

- Add vitepress-plugin-mermaid for diagram rendering
- Add Pentest Architecture page to sidebar nav
- Fix image paths (../public/ → / for VitePress public serving)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/.vitepress/config.mts

@@ -1,6 +1,7 @@
 import { defineConfig } from 'vitepress'
+import { withMermaid } from 'vitepress-plugin-mermaid'
 
-export default defineConfig({
+export default withMermaid(defineConfig({
   title: 'Certifai',
   description: 'AI-powered security compliance scanning platform',
   ignoreDeadLinks: [
@@ -31,6 +32,7 @@ export default defineConfig({
           { text: 'Dashboard Overview', link: '/features/overview' },
           { text: 'DAST Scanning', link: '/features/dast' },
           { text: 'AI Pentest', link: '/features/pentest' },
+          { text: 'Pentest Architecture', link: '/features/pentest-architecture' },
           { text: 'AI Chat', link: '/features/ai-chat' },
           { text: 'Code Knowledge Graph', link: '/features/graph' },
           { text: 'MCP Integration', link: '/features/mcp-server' },
@@ -51,4 +53,5 @@ export default defineConfig({
       message: 'Certifai Documentation',
     },
   },
-})
+  mermaid: {},
+}))