Migrated from spboyer/waza#387

Summary

Design how eval.yaml can reference remote graders via Go-module-style paths.

Concept

graders:
  - ref: github.com/waza-evals/fact@v1.0
  - ref: github.com/myorg/custom-grader@v2.1
    config:
      threshold: 0.8

Design Questions

• How does waza get resolve and cache remote graders?
• Version pinning semantics (exact, range, latest)?
• Offline/air-gapped fallback from local cache?
• How to handle transitive dependencies (grader A depends on dataset B)?
• Authentication for private repos?

Parent: #385