site: Add official website source

- Set VitePress base to '/docs/' for serving documentation at /docs/ route
- Update favicon path in head config to '/docs/favicon.ico'
- Add build:site script to build website and docs, then merge outputs

docs/.vitepress/config.ts

@@ -3,9 +3,10 @@ import { defineConfig } from 'vitepress'
 export default defineConfig({
   title: 'HAPI',
   description: 'Control your AI agents from anywhere',
+  base: '/docs/',
 
   head: [
-    ['link', { rel: 'icon', href: '/favicon.ico' }],
+    ['link', { rel: 'icon', href: '/docs/favicon.ico' }],
   ],
 
   themeConfig: {