The schema description and the README both pointed at MODEL_SPEC.md in the
GitHub repository and called it the source of truth. That file does not exist
on main; these artifacts are the spec.
Let a variant's methods nest under its components
A multi-component variant could only declare one flat methods map, so a
pipeline whose parts share a method name had nowhere to put them: supertonic
has four forwards, kokoro two. A methods value may now be either a signature
or a map of signatures keyed by method name, selected by component.
Purely additive: every config that validated before still validates.
