fix: pass truck centroid to batch manager for state transitions

The legacy batch_mgr.update() method was calling update_truck() with
truck_centroid=None, which prevented the batch from transitioning
from IDLE to TRUCK_STABILIZING (centroid must be non-None).

Now pipeline computes centroid from ROI and passes it through.

Verified: old run had 0 cyan pixels (no tracking), new run has 28190
cyan pixels (tracking active, bounding boxes drawn).

src/batch.py

@@ -266,10 +266,11 @@ class BatchLifecycleManager:
         timestamp: float,
         loading_count: int = 0,
         unloading_count: int = 0,
+        truck_centroid: tuple[float, float] | None = None,
     ) -> None:
         """Legacy update method — kept for backward compatibility."""
         if self._state in (BatchState.IDLE, BatchState.TRUCK_STABILIZING):
-            self.update_truck(truck_detected, None, timestamp)
+            self.update_truck(truck_detected, truck_centroid, timestamp)
         elif self._state in (BatchState.COUNTING_SACKS, BatchState.WAITING_FOR_ACTIVITY):
             self.update_sacks(
                 has_crossing_event=False,

src/pipeline.py

@@ -184,12 +184,17 @@ def run_pipeline(
                 counter.line_x_end = roi.x2
 
             # Batch lifecycle
+            truck_centroid = None
+            if roi is not None:
+                truck_centroid = ((roi.x1 + roi.x2) / 2.0, (roi.y1 + roi.y2) / 2.0)
+
             if frame_idx % truck_det_interval == 0:
                 batch_mgr.update(
                     truck_detected=truck_present,
                     timestamp=timestamp,
                     loading_count=counter.loading_count,
                     unloading_count=counter.unloading_count,
+                    truck_centroid=truck_centroid,
                 )
 
             # Track → Stabilize → Count