Default npm run build command no longer needs to build the packages

### Description

Now that we build the apps from source rather than inlining the dist there's no need for the `npm run build` command to build each package independently.

- Make sure CI still works and checks the packages build
- Make sure self hosters and staging can still build from source (and it should be quicker now!)
- Make sure publishing the npm packages still works
- Consider removing turbo which is not very useful any more

Start by inspecting the npm run build configuration and the CI, self-hosting, staging, and npm publishing workflows. Verify that CI still checks package builds, source builds work for self-hosters and staging, and npm packages still publish successfully; then assess whether turbo can be removed.

Written by the indexing model from the issue text.