Curation tiers

Tier	Meaning
L0	Scaffold gaps (missing KG JSON)
L1	KG present, config incomplete
L2	Strict validation pass (pipeline-ready)
L3	Expression-curated
Reference / CI-validated	Deeper maintained sets

v0.1.0: 88 L2 strict, 6 reference, 8 CI-validated. Full playbook: disease-curation.md.