CFFDRS API: Hello World

**Describe the task**
First baby step towards making our own CFFDRS API microservice.

**Acceptance Criteria**
- [ ] Uses FastAPI to create an app that says "Hello world"
- [ ] Deploys all the way through to prod with GH Actions
- [ ] The project will have to be licensed as GPL to comply with the CFFDRS license.
- [ ] Using a familiar stack with poetry + python + fastapi

**Additional context**
- Stick with our existing stack for now because it's familiar
- In anticipation of using Python implementation in CFF API instead of R package

Start by reviewing the repository's existing Python and GitHub Actions structure, then identify where a Poetry-managed FastAPI service and its production deployment belong. Confirm the GPL licensing requirement and define the production target before implementation. Done means a FastAPI app responds with "Hello world" and the service deploys to production through GitHub Actions.

Written by the indexing model from the issue text.