Fix NameError in cluster nodes API

- Fixed undefined variable 'local_gpu_backends' in api_cluster_nodes function
- Properly defined local_available_backends, local_gpu_backends, and local_cpu_backends
- Updated local node detection to show nodes with any available backends (GPU or CPU)
- Ensured CPU-only nodes are correctly identified and displayed
- Maintained backward compatibility with existing GPU-only node detection

vidai/web.py

@@ -486,10 +486,12 @@ def api_cluster_nodes():
         nodes.append(node_data)
 
     # Detect and aggregate local worker processes on master
-    # Only show local node if GPU backends are available
+    # Show local node if any backends are available (GPU or CPU)
     from vidai.compat import get_available_backends
-    local_available_gpu_backends = [b for b in get_available_backends() if b in ['cuda', 'rocm']]
-    if local_available_gpu_backends:
+    local_available_backends = get_available_backends()
+    local_gpu_backends = [b for b in local_available_backends if b in ['cuda', 'rocm']]
+    local_cpu_backends = [b for b in local_available_backends if b == 'cpu']
+    if local_available_backends:
         local_workers = detect_local_workers()
         if local_workers:
             # Group local workers by type