fix: update docstring example to use Agent() constructor pattern

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: Prachig-Microsoft

src/ContentProcessorWorkflow/src/libs/agent_framework/agent_speaking_capture.py

@@ -68,7 +68,8 @@ async def async_callback(capture_data: dict):
         # Without callback (store only)
         capture_middleware = AgentSpeakingCaptureMiddleware()
 
-        agent = client.create_agent(
+        agent = Agent(
+            client=client,
             name="MyAgent",
             middleware=[capture_middleware],
             ...