Move kube (client, apply, exec, secrets, kustomize_build) into kube/
submodule with tools.rs as a child. Move openbao BaoClient into
openbao/ submodule.
Convert the single binary crate into a Cargo workspace with two members:
sunbeam-sdk (library) and sunbeam (thin binary). Moves build.rs to the
SDK with adjusted .git/HEAD path for the nested layout.