Fix cluster nodes sorting error

- Handle timestamp strings in sorting function
- Parse ISO timestamp strings to numeric values for proper sorting
- Prevent TypeError when sorting by last_seen timestamp

vidai/web.py

@@ -641,7 +641,19 @@ def api_cluster_nodes():
             nodes.append(local_node)
 
     # Sort: active first, then by last_seen desc
-    nodes.sort(key=lambda x: (not x['connected'], -x['last_seen']))
+    def sort_key(node):
+        connected = node['connected']
+        last_seen = node.get('last_seen', 0)
+        if isinstance(last_seen, str):
+            try:
+                # Parse timestamp string to float
+                import datetime
+                last_seen = datetime.datetime.fromisoformat(last_seen.replace('Z', '+00:00')).timestamp()
+            except:
+                last_seen = 0
+        return (not connected, -last_seen)
+
+    nodes.sort(key=sort_key)
 
     # Cluster master stats
     from .cluster_master import cluster_master