feat: config-authoritative conf gates + cross-model IoU sack suppression

tests/test_config_loader.py

@@ -84,6 +84,7 @@ def test_counting_knobs_match_production_defaults(repo_config_path):
     assert c.exit_overlap_threshold == 0.05
     assert c.camera_noise_deadband == 50
     assert c.duplicate_circle_radius == 30
+    assert c.cross_class_iou == 0.4
     assert c.min_valid_area == 15000
     assert c.max_reid_transit_distance == 400
     assert c.circle_stay_timeout_sec == 10.0