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/packages/azurefunctions/tests/test_app.py

@@ -12,7 +12,7 @@ from unittest.mock import ANY, AsyncMock, Mock, patch
 import azure.durable_functions as df
 import azure.functions as func
 import pytest
-from agent_framework import AgentResponse, ChatMessage
+from agent_framework import AgentResponse, Message
 from agent_framework_durabletask import (
     MIMETYPE_APPLICATION_JSON,
     MIMETYPE_TEXT_PLAIN,
@@ -356,7 +356,7 @@ class TestAgentEntityOperations:
         """Test that entity can run agent operation."""
         mock_agent = Mock()
         mock_agent.run = AsyncMock(
-            return_value=AgentResponse(messages=[ChatMessage(role="assistant", text="Test response")])
+            return_value=AgentResponse(messages=[Message(role="assistant", text="Test response")])
         )
 
         entity = AgentEntity(mock_agent, state_provider=_InMemoryStateProvider(thread_id="test-conv-123"))
@@ -373,9 +373,7 @@ class TestAgentEntityOperations:
     async def test_entity_stores_conversation_history(self) -> None:
         """Test that the entity stores conversation history."""
         mock_agent = Mock()
-        mock_agent.run = AsyncMock(
-            return_value=AgentResponse(messages=[ChatMessage(role="assistant", text="Response 1")])
-        )
+        mock_agent.run = AsyncMock(return_value=AgentResponse(messages=[Message(role="assistant", text="Response 1")]))
 
         entity = AgentEntity(mock_agent, state_provider=_InMemoryStateProvider(thread_id="conv-1"))
 
@@ -407,9 +405,7 @@ class TestAgentEntityOperations:
     async def test_entity_increments_message_count(self) -> None:
         """Test that the entity increments the message count."""
         mock_agent = Mock()
-        mock_agent.run = AsyncMock(
-            return_value=AgentResponse(messages=[ChatMessage(role="assistant", text="Response")])
-        )
+        mock_agent.run = AsyncMock(return_value=AgentResponse(messages=[Message(role="assistant", text="Response")]))
 
         entity = AgentEntity(mock_agent, state_provider=_InMemoryStateProvider(thread_id="conv-1"))
 
@@ -448,9 +444,7 @@ class TestAgentEntityFactory:
     def test_entity_function_handles_run_operation(self) -> None:
         """Test that the entity function handles the run operation."""
         mock_agent = Mock()
-        mock_agent.run = AsyncMock(
-            return_value=AgentResponse(messages=[ChatMessage(role="assistant", text="Response")])
-        )
+        mock_agent.run = AsyncMock(return_value=AgentResponse(messages=[Message(role="assistant", text="Response")]))
 
         entity_function = create_agent_entity(mock_agent)
 
@@ -475,9 +469,7 @@ class TestAgentEntityFactory:
     def test_entity_function_handles_run_agent_operation(self) -> None:
         """Test that the entity function handles the deprecated run_agent operation for backward compatibility."""
         mock_agent = Mock()
-        mock_agent.run = AsyncMock(
-            return_value=AgentResponse(messages=[ChatMessage(role="assistant", text="Response")])
-        )
+        mock_agent.run = AsyncMock(return_value=AgentResponse(messages=[Message(role="assistant", text="Response")]))
 
         entity_function = create_agent_entity(mock_agent)