Per the consolidation onto El: 'crates' is the Rust word, 'vessel' is
El's (per spec/language.md §15). The directory rename is the structural
marker that this slot holds an El buildable unit, even if its current
contents are still Rust pending port.
Mechanical: git mv crates vessels, sed workspace members and any path
dependencies, update CI workflow paths, update README references.
Cross-repo path dependencies (`../foo/crates/bar`) updated workspace-
wide so cargo metadata still resolves where the Rust still builds.
Will Anderson