v0.1.0

First release: the three-stage GBD disability-weight estimator (Salomon et al. 2012 replication) with loud identification gates, respondent-cluster bootstrap (coverage-tested), multi-survey pooling, held-out fit diagnostics, and the full synthetic validation program (recovery, metamorphic, misspecification, power, GBD-2010-scale). Methods guide with citations: https://welfareweights.github.io/engine/methods.pdf - evidence summary in docs/VALIDATION.md, changelog in CHANGELOG.md.