Move `task=classify` with `mode=track` warning to tracker `on_predict_start` (#18837)

Co-authored-by: UltralyticsAssistant <web@ultralytics.com>

ultralytics/cfg/__init__.py

@@ -921,12 +921,7 @@ def entrypoint(debug=""):
     # Task
     task = overrides.pop("task", None)
     if task:
-        if task == "classify" and mode == "track":
-            raise ValueError(
-                f"❌ Classification doesn't support 'mode=track'. Valid modes for classification are"
-                f" {MODES - {'track'}}.\n{CLI_HELP_MSG}"
-            )
-        elif task not in TASKS:
+        if task not in TASKS:
             if task == "track":
                 LOGGER.warning(
                     "WARNING ⚠️ invalid 'task=track', setting 'task=detect' and 'mode=track'. Valid tasks are {TASKS}.\n{CLI_HELP_MSG}."

ultralytics/trackers/track.py

@@ -31,6 +31,9 @@ def on_predict_start(predictor: object, persist: bool = False) -> None:
         >>> predictor = SomePredictorClass()
         >>> on_predict_start(predictor, persist=True)
     """
+    if predictor.args.task == "classify":
+        raise ValueError("❌ Classification doesn't support 'mode=track'")
+
     if hasattr(predictor, "trackers") and persist:
         return