Add basic Guider project and remove Nuxt content

pages/404.tsx

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+import { createNotFoundPage } from '@neato/guider/client';
+
+export default createNotFoundPage();

pages/_app.tsx

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+import '@neato/guider/style.css';
+import { createGuiderApp } from '@neato/guider/client';
+
+export default createGuiderApp();

pages/index.mdx

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+# Hello world
+This is my first `@neato/guider` page!