fix: remove /hatk/ base path now that docs are on custom domain

Co-Authored-By: Claude Opus 4.6 <[e-mail]>

docs/site/.vitepress/config.ts

···
 import { defineConfig } from 'vitepress'
 
 export default defineConfig({
-  base: '/hatk/',
+  base: '/',
   title: 'hatk',
   description: 'Build AT Protocol applications with typed XRPC endpoints.',