d1: DART dropout trees on LightGBM in GA loop — expected Brier delta -0.0025

P012: Add boosting_type=dart, drop_rate=0.1, skip_drop=0.5, uniform_drop=True
to LGBMClassifier in _build_model (genetic_loop_v3.py). DART prevents first-tree
dominance, improves probability spread across [0.3,0.7], reduces reliability
component of Brier. Consistent with Rashmi & Gilad-Bachrach 2015 (AISTATS).
Already verified working in app.py stacking path — now applied to main GA loop.

evolution/genetic_loop_v3.py

@@ -1107,6 +1107,8 @@ def _build_model(hp, use_gpu=False):
                 num_leaves=min(2 ** hp["max_depth"] - 1, 127),
                 reg_alpha=hp["reg_alpha"],
                 reg_lambda=hp["reg_lambda"],
+                # DART P012: dropout trees — better probability calibration, reduces reliability error
+                boosting_type="dart", drop_rate=0.1, skip_drop=0.5, uniform_drop=True,
                 verbose=-1, random_state=42, n_jobs=-1,
             )
         elif mt == "catboost":