[FR-004] Orchestrator stores raw + normalized output as content-addressed artifacts

[explosivebit]

Trace: PRD prd-v0-1-smoke-evaluation-run · FR-004 · SPEC spec-manifest-eval-artifact-contracts-smoke-v0-1 (ArtifactRef schema)

Capability: Every eval output stored at artifacts/runs/{run_hash}/evals/{eval_id}/{type}-{sha256}.{ext}. Manifest artifact_refs carries sha256 + size_bytes + uri + mime_type.

Acceptance:

• AC-3 from SPEC: sha256 of stored raw_output matches artifact_refs.raw_output.sha256
• Normalization (strip greetings/signatures) deterministic