Python: DevUI Fix Serialization, Timestamp and Other Issues (#1584)

* refactor(devui): adopt standard OpenAI lifecycle events for agents and workflows

- Replace custom workflow events with OpenAI Responses API standard lifecycle events
- Add AgentStartedEvent, AgentCompletedEvent, AgentFailedEvent for clean separation
- Implement ExecutorActionItem for workflow executor tracking
- Convert informational events to trace events to reduce noise
- Update README mapper table with comprehensive event mappings
- Maintain full backward compatibility with legacy events

* fix(devui): resolve timestamp overwriting and Content serialization errors

- Fix tool call timestamps being overwritten on each render (#1483)
- Add recursive Content serialization to handle ChatMessage and nested objects (#1548)
- Implement proper MCP tool cleanup on server shutdown
- Add timestamp field to function_result.complete events
- Enhance credential and client resource cleanup

Fixes #1483, #1548
Partial improvements for #1476

python/packages/devui/frontend/src/App.tsx

@@ -241,6 +241,8 @@ export default function App() {
 
   // Show error state if loading failed
   if (entityError) {
+    const currentBackendUrl = apiClient.getBaseUrl();
+
     return (
       <div className="h-screen flex flex-col bg-background">
         <AppHeader
@@ -290,7 +292,7 @@ export default function App() {
 
               <p className="text-xs text-muted-foreground">
                 Default:{" "}
-                <span className="font-mono">http://localhost:8080</span>
+                <span className="font-mono">{currentBackendUrl}</span>
               </p>
             </div>