The backend-agnostic, GPU-free render-prep layer. Holds the
RenderBackend/SceneControl trait seam the device backends implement, plus
the record builders, render graph, and CPU-side math that turn asset
components into GPU-ready data. Depends on the vocabulary and the CPU compute
over it (concinnity-core); owns no device or window handle. The device
backends (concinnity-device) and the runtime driver (concinnity-engine) both
build on top of this crate.
The vulkan feature forwards a backend cfg and pulls in no dependency, so it
does not move the crate off that tier.