shigoto-types — typed primitives every other shigoto crate consumes.
Spec: theory/SHIGOTO.md §III.1–III.4 + §III.11–III.12.
v0.1.0 is the scaffold: trait + enum + struct surfaces declared,
implementations land as the bootstrap consumer (tend) migrates
per theory/SHIGOTO.md §IV.3 (M0.9 in the broader plan).