docs(next): fix the quick start to use getPageData

1. The Next quick start destructures Page from createNextApp, which only returns getPageData, generateMetadata and generateStaticParams, so following it fails to build.
2. The docs now show a page.tsx that calls getPageData and renders PageRenderer, and a client layout with NextAppProvider that no longer wraps <html> and <body>.
3. Fixes #380. Builds on #402.

Co-authored by @Jassi2004, based on #402.

Before

Building an app from the quick start fails with "Property 'Page' does not exist", and the dev server returns a 500.

https://github.com/user-attachments/assets/e660baeb-6610-44f3-85e3-95efb22c517c

After

The same steps from the fixed docs build, and the page renders the spec.

https://github.com/user-attachments/assets/1c69080f-6afa-4e69-baea-324b6ddd468a