Unclear documentation on build support

I have setup a nextjs project and successfully deployed to Firebase. However when the GitHub action runs it's missing the default npm build that's recommended in the cli setup flow. Trying to resolve this has left me very confused about what the cli is doing and what I need to do. There's a lot of magic and I can't seem to find any documentation explaining it.

Do I need to run next build myself? If I wanted to add additional steps into the build process when and how can I do this?

Additionally if I want to modify the build in future so I can tie together infrastructure changes e.g. with terraform are there any hooks so I can do it incrementally?

It would also be nice to know what functions get generated, e.g. is it one per route etc.

Thanks for all the great work.

Start by tracing the GitHub Action and CLI setup flow described in the issue, then document whether `next build` runs automatically and how additional build steps or infrastructure hooks are configured. Cover incremental Terraform-related changes and explain what generated functions correspond to routes; done means the documentation answers each question with a reproducible setup.

Written by the indexing model from the issue text.