Fix NameError: name 'os' is not defined in cluster_client.py

- Added missing import os at the top of vidai/cluster_client.py
- Removed redundant local import os in _handle_model_transfer_complete function
- This fixes the error when handling master commands on client receiving a job

vidai/cluster_client.py

@@ -19,6 +19,7 @@ Cluster client for distributed Video AI processing.
 Connects to cluster master and acts as a bridge for local subprocesses.
 """
 
+import os
 import socket
 import json
 import threading
@@ -435,7 +436,6 @@ class ClusterClient:
 
         if len(model_data) == expected_size:
             # Save the model file
-            import os
             os.makedirs('models', exist_ok=True)
             model_file = f"models/{model_path.replace('/', '_')}.bin"
             with open(model_file, 'wb') as f: