Python: [BREAKING] Simplify API: ChatAgent -> Agent, ChatMessage -> Message (#3747)

* [BREAKING] Rename ChatAgent -> Agent, ChatMessage -> Message, ChatClientProtocol -> SupportsChatGetResponse

Simplify the public API by removing redundant 'Chat' prefix from core types:
- ChatAgent -> Agent
- RawChatAgent -> RawAgent
- ChatMessage -> Message
- ChatClientProtocol -> SupportsChatGetResponse

Also renamed internal WorkflowMessage (was Message in _runner_context) to avoid collision.

No backward compatibility aliases - this is a clean breaking change.

* [BREAKING] Rename Agent chat_client parameter to client

* Fix rebase issues: WorkflowMessage references and broken markdown links

* Fix formatting and lint issues from code quality checks

* Fix import ordering in workflow sample files

* fixed rebase

* Fix test failures: use WorkflowMessage and A2AMessage after ChatMessage→Message rename

- Replace Message(data=..., source_id=...) with WorkflowMessage(...) in workflow tests
- Fix isinstance check in A2A agent to use A2AMessage instead of Message
- Fix import in test_workflow_observability.py (Message→WorkflowMessage)

* Fix lint, fmt, and sample errors after ChatMessage→Message rename

- Auto-fix 70+ ruff lint issues across samples (ChatMessage→Message refs)
- Fix HostedVectorStoreContent→Content.from_hosted_vector_store in file search sample
- Fix _normalize_messages→normalize_messages in custom agent sample
- Fix context.terminate→raise MiddlewareTermination in middleware samples
- Fix with_update_hook→with_transform_hook in override middleware sample
- Add TOptions_co import back to custom_chat_client sample
- Add noqa for FastAPI File() default in chatkit sample
- Fix B023 loop variable capture in weather agent sample

* fix: update Agent constructor calls from chat_client to client in declaration-only tool tests

* fix: add register_cleanup to devui lazy-loading proxy and type stub

* fixed tests and updated new pieces

* fix agui typevar

* fix merge errors

* fix merge conflicts

* fiux merge

* Remove unused links

---------

Co-authored-by: Evan Mattson <evan.mattson@microsoft.com>

python/samples/autogen-migration/orchestrations/04_magentic_one.py

@@ -21,7 +21,7 @@ from typing import cast
 
 from agent_framework import (
     AgentResponseUpdate,
-    ChatMessage,
+    Message,
     WorkflowEvent,
 )
 from agent_framework.orchestrations import MagenticProgressLedger
@@ -129,7 +129,7 @@ async def run_agent_framework() -> None:
 
         elif event.type == "magentic_orchestrator":
             print(f"\n[Magentic Orchestrator Event] Type: {event.data.event_type.name}")
-            if isinstance(event.data.content, ChatMessage):
+            if isinstance(event.data.content, Message):
                 print(f"Please review the plan:\n{event.data.content.text}")
             elif isinstance(event.data.content, MagenticProgressLedger):
                 print(f"Please review progress ledger:\n{json.dumps(event.data.content.to_dict(), indent=2)}")
@@ -150,7 +150,7 @@ async def run_agent_framework() -> None:
     print("Final Output:")
     # The output of the Magentic workflow is a list of ChatMessages with only one final message
     # generated by the orchestrator.
-    output_messages = cast(list[ChatMessage], output_event.data)
+    output_messages = cast(list[Message], output_event.data)
     if output_messages:
         output = output_messages[-1].text
         print(output)