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>