feat(cli): accept digest-only attribution evidence

[tcconnally]

Summary

• Expose optional evidence hash, policy version, result hash, human review, and correction reference fields on ledger meter.
• Forward these fields to existing decision-context storage.

Privacy

• Metadata and hashes only.
• No prompt, draft, customer, credential, or cost data added.

Validation

• End-to-end local CLI validation persisted all four attribution fields.
• SHA-256 integrity chain verified.