Metis: define registry YAML schemas

[SaJaToGu]

Parent: #478

Goal

Define initial YAML schemas for Metis worker, model and hardware registries.

Scope

• Add schema documents for worker, model and hardware registry entries.
• Keep the schema simple enough for milestone 0.1.
• Align fields with the existing docs and examples/home-cluster.yaml.

Acceptance Criteria

• Worker schema covers id, role, hardware, status, wake behavior and capabilities.
• Model schema covers provider, runtime, capabilities, requirements and cost profile.
• Hardware schema covers CPU, memory, GPU, storage, power profile and network traits.
• Example configuration can be mapped to the schema without changing the documented concept.

[SaJaToGu]

Migrated to https://github.com/SaJaToGu/metis/issues/9 — Registry YAML schemas. This AIS issue stays open until the user verifies the migration.