MCMC SBS Bayesian evaluation produces inverted AUC after optimization changes

[eprifti]

test_mcmc_with_sbs produces AUC 0.21 (inverted). The LASSO prescreen + batch elimination + adaptive n_iter changes broke the SBS posterior quality. The BTR conversion works fine but the raw Bayesian model evaluation (bayesian_compute_roc_and_metrics) fails. Test ignored pending fix.