Improve types and docs around FastAPI Http Endpoints

Some users want to directly use the Http endpoints from the FastAPI server. We should improve the naming, types, docstrings, and docs around this.

@HammadB @atroyn how would we feel about make this more of a "external service"? I know in the past we have thought of it as more "internal"

http://localhost:8000/docs exists, but we can do better.

Start at the FastAPI server and its generated http://localhost:8000/docs page, then review the HTTP endpoint names, types, docstrings, and surrounding documentation. Clarify whether the endpoints are intended as an external service; done means the public-facing naming, typing, and documentation consistently support direct use.

Written by the indexing model from the issue text.