Fix cluster client GPU detection - extract backends from capabilities

- Fix cluster master to properly detect GPU backends from client capabilities
- Extract available_backends from capabilities list instead of gpu_info
- Ensure clients with GPU workers are correctly identified as GPU-enabled

vidai/cluster_master.py

@@ -204,12 +204,15 @@ class ClusterMaster:
         # Generate client ID from token
         client_id = hashlib.sha256(token.encode()).hexdigest()[:16]
 
-        # Check GPU capabilities for logging
-        gpu_info = client_info.get('gpu_info', {})
-        available_backends = gpu_info.get('available_backends', [])
+        # Extract available backends from capabilities
+        capabilities = client_info.get('capabilities', [])
+        available_backends = list(set(cap.split('_')[1] for cap in capabilities if '_' in cap and len(cap.split('_')) > 1))
         gpu_backends = [b for b in available_backends if b in ['cuda', 'rocm']]
         has_gpu = len(gpu_backends) > 0
 
+        # Get GPU info for storage
+        gpu_info = client_info.get('gpu_info', {})
+
         # Get hostname and IP
         hostname = client_info.get('hostname', 'unknown')
         # Try to get real IP address from websocket