Remove shared tracker between cameras, fix task warning, add export script

- Remove shared DetectionTracker across cameras to prevent state leakage
- Add task="detect" to YOLO constructor to suppress warning
- Add export_engine.py script for .pt to .engine conversion
- Regenerate ONNX and TensorRT engine with latest settings

src/chicken_counter/batch_runner.py

@@ -10,7 +10,6 @@ from chicken_counter.compress import compress_video_to_target
 from chicken_counter.config import BatchSettings, build_camera_config_from_batch
 from chicken_counter.pipeline import run_pipeline
 from chicken_counter.report import build_batch_report, persist_batch_reports
-from chicken_counter.tracking import DetectionTracker
 from chicken_counter.types import CameraBatchResult
 
 
@@ -29,20 +28,6 @@ def run_daily_batch(settings: BatchSettings, date: str | None = None, *, verbose
     discovery = discover_camera_videos(day_dir, settings)
     camera_order = sorted(settings.cameras.items(), key=lambda item: item[1].camera_num)
 
-    first_camera_id = next(
-        camera_id for camera_id, _preset in camera_order if camera_id in discovery.found
-    )
-    first_source = discovery.found[first_camera_id]
-    init_output_path = output_dir / f"{first_camera_id}_vis.mp4" if not no_video else None
-    init_config = build_camera_config_from_batch(
-        settings,
-        first_camera_id,
-        source=first_source,
-        output_path=init_output_path,
-        checkpoint_dir=output_dir / "checkpoints" / first_camera_id,
-    )
-    shared_tracker = DetectionTracker(init_config)
-
     camera_results: list[CameraBatchResult] = []
     report_path = output_dir / f"counts_{run_date}.json"
 
@@ -73,7 +58,7 @@ def run_daily_batch(settings: BatchSettings, date: str | None = None, *, verbose
             checkpoint_dir=checkpoint_dir,
         )
         camera_config.performance.verbose = verbose
-        pipeline_result = run_pipeline(camera_config, tracker=shared_tracker, show_progress=show_progress)
+        pipeline_result = run_pipeline(camera_config, show_progress=show_progress)
         camera_results.append(
             CameraBatchResult(
                 camera_id=camera_id,

src/chicken_counter/tracking.py

@@ -17,7 +17,7 @@ class DetectionTracker:
         self.config = config
         model_path = Path(config.detection.model_path)
         self.model_kind = model_path.suffix.lower().lstrip(".") or "unknown"
-        self.model = YOLO(config.detection.model_path)
+        self.model = YOLO(config.detection.model_path, task="detect")
         self.tracker_config_path = str(Path(config.tracker.tracker_config_path))
         self.verbose = config.performance.verbose
         self._infer_count = 0
@@ -47,7 +47,6 @@ class DetectionTracker:
             offset_x, offset_y = x1, y1
 
         track_kwargs: dict = {
-            "task": "detect",
             "source": source,
             "persist": self.config.tracker.persist,
             "tracker": self.tracker_config_path,