fix(vercel): support custom baseURL

[danielroe]

🔗 Linked issue

resolves nuxt/nuxt#26886
resolves nuxt/nuxt#21780
resolves #1348

❓ Type of change

• 📖 Documentation (updates to the documentation, readme, or JSdoc annotations)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• 🧹 Chore (updates to the build process or auxiliary tools and libraries)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

It's possible to deploy sites to Vercel with a custom baseURL and the renderer will correctly handle 404 on / and correct responses from /<baseURL>/ but the public assets aren't configured to respect the baseURL.

Published minimal reproduction & patch to https://github.com/danielroe/nuxt-3-vercel-baseurl-test - you can see deployed at https://nuxt-3-vercel-baseurl-test-tan.vercel.app/subdir.

You can confirm that correct headers are added to a request like:

http --headers https://nuxt-3-vercel-baseurl-test-tan.vercel.app/subdir/_nuxt/C7CLbNSw.js
> HTTP/1.1 200 OK
> Access-Control-Allow-Origin: *
> Age: 88
> Cache-Control: public,max-age=31536000,immutable
> Connection: keep-alive
> Content-Disposition: inline; filename="C7CLbNSw.js"
> Content-Encoding: gzip
> Content-Type: application/javascript; charset=utf-8
> Date: Thu, 23 May 2024 16:37:55 GMT
> Etag: W/"c44aff3c70a5f49fad126ee0c615c297"

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[pi0]

Thanks for carefully testing it ❤️