fix: graceful error when onnxruntime missing for .onnx models

src/pipeline.py

@@ -92,6 +92,17 @@ def run_pipeline(
     effective_filter = class_filter or (
         model_config.known_classes if model_config.known_classes else None
     )
+
+    # Check onnxruntime for .onnx models
+    if model_config.path.endswith(".onnx"):
+        try:
+            import onnxruntime  # noqa: F401
+        except ImportError:
+            raise RuntimeError(
+                f"onnxruntime is not installed. Cannot load .onnx model '{model_config.filename}'. "
+                f"Either install it (pip install onnxruntime) or use the .engine version of this model."
+            )
+
     shared_model = YOLO(model_config.path)
     detector = BaseDetector(
         shared_model, conf=sack_conf, class_filter=effective_filter