Metis: add static registry loader

[SaJaToGu]

Parent: #478

Goal

Add a minimal static registry loader for Metis configuration files.

Scope

• Load YAML configuration from examples/home-cluster.yaml or a caller-provided path.
• Return structured worker entries.
• Avoid production database work.
• Keep the implementation small and testable.

Acceptance Criteria

• Loader reads the example config.
• Loader validates required top-level worker fields.
• Missing or malformed files produce clear errors.
• Tests cover the happy path and one invalid config.

[SaJaToGu]

Migrated to https://github.com/SaJaToGu/metis/issues/5 — Static registry loader. This AIS issue stays open until the user verifies the migration.