RAG Phase 3: RAG eval in the shared #205 eval package

[VforVitorio]

Sub of Epic #318. documents/audits/AUDIT_RAG_LAYER.md Phase 3 (size M).

Scope: RAG eval inside the shared src/strategy/eval/ package (#205), not a parallel one.

• Wire a reproducible RAG retrieval eval: ~30 queries including the 3 production question shapes, computing P@k / MRR + a wrong-year rate + a citation-match rate. Revives the one-shot unwired N30B notebook (ML-eval E-11).

Deliverable: f1-eval rag (via the shared harness) reports retrieval quality + wrong-year + citation-match over a fixed query set.