Distribution-change attribution — Y intercept shift

Suite path: conformance/attribution/distribution_change_y_shift

Synthetic linear SCM X → Y. Baseline (rows 0..40): Y = 1 + 2X. Comparison (rows 40..80): Y = 6 + 2X. Exact Shapley should attribute the mean shift primarily to the Y mechanism.

Expected summary

Top-level keys: allocation, dominant_component, notes, outcome, total_change_min (5 fields).