This PR adds Storyteller.ai API integration for saving and loading
Storyteller Studio scenes to/from the backend.
### Known issues
* The skybox is not currently stored in the serialized scene format
This PR adds `cargo fmt -- --check`, `nx lint ...` and `nx test ...` as
GitHub Actions. This will cause future PRs to automatically fail when
formatting issues, Clippy warnings, or test failures are present in the
changed code.