fix(api_server): update tool_progress_callback signature for Open WebUI streaming

Commit cc2b56b2 changed the tool_progress_callback signature from
(name, preview, args) to (event_type, name, preview, args, **kwargs)
but the API server's chat completion streaming callback was not updated.

This caused tool calls to not display in Open WebUI because the
callback received arguments in wrong positions.

- Update _on_tool_progress to use new 4-arg signature
- Add event_type filter to only show tool.started events
- Add **kwargs for optional duration/is_error parameters

gateway/platforms/api_server.py

@@ -564,8 +564,10 @@ class APIServerAdapter(BasePlatformAdapter):
                 if delta is not None:
                     _stream_q.put(delta)
 
-            def _on_tool_progress(name, preview, args):
+            def _on_tool_progress(event_type, name, preview, args, **kwargs):
                 """Inject tool progress into the SSE stream for Open WebUI."""
+                if event_type != "tool.started":
+                    return  # Only show tool start events in chat stream
                 if name.startswith("_"):
                     return  # Skip internal events (_thinking)
                 from agent.display import get_tool_emoji