chore: add unstable_runtimeJS to speed prerender app

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What does this PR do?

🤖 Generated by Copilot at c753fb2

This pull request disables the runtime JavaScript for two page components, posts/[id].tsx and u/[handle].tsx, in the prerender app. This improves the performance and SEO of these pages, as they only render static content.

Related issues

Fixes # (issue)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Enhancement (non-breaking small changes to existing functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Explanation of the changes

🤖 Generated by Copilot at c753fb2

• Disable runtime JavaScript for two static pages (config in link and link)

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Name	Status	Preview	Updated (UTC)
prerender	✅ Ready (Inspect)	Visit Preview	Apr 8, 2023 1:45pm
web	✅ Ready (Inspect)	Visit Preview	Apr 8, 2023 1:45pm