Feat: Updates output.mdx docs to clarify standalone output usage

[simonorzel26]

What?

Clarifies standalone output documentation regarding confusion in: https://github.com/vercel/next.js/issues/49283 https://stackoverflow.com/questions/76506072/standalone-next-js-server-returns-404-for-static-content-unless-next-start-is-ca https://www.reddit.com/r/nextjs/comments/18t6ltd/404s_for_public_and_static_content_in_standalone/

Why?

The standalone build needs the static assets to be moved in a specific folder before being ready to be served via server.js. Unfortunately it isn't so clear sometimes, as the .next/static assets need to be in the same directory as the server.js. This is not always easy to tell, and debug, as with monorepos, the build ofter puts server.js into a nested directory.

[ijjk]

Allow CI Workflow Run

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[ijjk]

Allow CI Workflow Run

• [ ] approve CI run for commit: 82663c3fb3aa2843211882db41d0945a356999ba

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer