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/chatkit/tests/test_converter.py

@@ -5,7 +5,7 @@
 from unittest.mock import Mock
 
 import pytest
-from agent_framework import ChatMessage
+from agent_framework import Message
 from chatkit.types import UserMessageTextContent
 
 from agent_framework_chatkit import ThreadItemConverter, simple_to_agent_input
@@ -43,7 +43,7 @@ class TestThreadItemConverter:
         result = await converter.to_agent_input(input_item)
 
         assert len(result) == 1
-        assert isinstance(result[0], ChatMessage)
+        assert isinstance(result[0], Message)
         assert result[0].role == "user"
         assert result[0].text == "Hello, how can you help me?"
 
@@ -110,13 +110,13 @@ class TestThreadItemConverter:
         assert result[0].text == "Hello world!"
 
     def test_hidden_context_to_input(self, converter):
-        """Test converting hidden context item to ChatMessage."""
+        """Test converting hidden context item to Message."""
         hidden_item = Mock()
         hidden_item.content = "This is hidden context information"
 
         result = converter.hidden_context_to_input(hidden_item)
 
-        assert isinstance(result, ChatMessage)
+        assert isinstance(result, Message)
         assert result.role == "system"
         assert result.text == "<HIDDEN_CONTEXT>This is hidden context information</HIDDEN_CONTEXT>"
 
@@ -288,7 +288,7 @@ class TestThreadItemConverter:
         assert message.contents[1].media_type == "application/pdf"
 
     def test_task_to_input(self, converter):
-        """Test converting TaskItem to ChatMessage."""
+        """Test converting TaskItem to Message."""
         from datetime import datetime
 
         from chatkit.types import CustomTask, TaskItem
@@ -302,7 +302,7 @@ class TestThreadItemConverter:
         )
 
         result = converter.task_to_input(task_item)
-        assert isinstance(result, ChatMessage)
+        assert isinstance(result, Message)
         assert result.role == "user"
         assert "Analysis: Analyzed the data" in result.text
         assert "<Task>" in result.text
@@ -347,7 +347,7 @@ class TestThreadItemConverter:
         result = converter.workflow_to_input(workflow_item)
         assert isinstance(result, list)
         assert len(result) == 2
-        assert all(isinstance(msg, ChatMessage) for msg in result)
+        assert all(isinstance(msg, Message) for msg in result)
         assert "Step 1: First step" in result[0].text
         assert "Step 2: Second step" in result[1].text
 
@@ -369,7 +369,7 @@ class TestThreadItemConverter:
         assert result is None
 
     def test_widget_to_input(self, converter):
-        """Test converting WidgetItem to ChatMessage."""
+        """Test converting WidgetItem to Message."""
         from datetime import datetime
 
         from chatkit.types import WidgetItem
@@ -384,7 +384,7 @@ class TestThreadItemConverter:
         )
 
         result = converter.widget_to_input(widget_item)
-        assert isinstance(result, ChatMessage)
+        assert isinstance(result, Message)
         assert result.role == "user"
         assert "widget_1" in result.text
         assert "graphical UI widget" in result.text
@@ -417,6 +417,6 @@ class TestSimpleToAgentInput:
         result = await simple_to_agent_input(input_item)
 
         assert len(result) == 1
-        assert isinstance(result[0], ChatMessage)
+        assert isinstance(result[0], Message)
         assert result[0].role == "user"
         assert result[0].text == "Test message"