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/devui/tests/devui/test_conversations.py

@@ -199,7 +199,7 @@ async def test_list_items_pagination():
 @pytest.mark.asyncio
 async def test_list_items_converts_function_calls():
     """Test that list_items properly converts function calls to ResponseFunctionToolCallItem."""
-    from agent_framework import ChatMessage, ChatMessageStore
+    from agent_framework import ChatMessageStore, Message
 
     store = InMemoryConversationStore()
 
@@ -216,8 +216,8 @@ async def test_list_items_converts_function_calls():
 
     # Simulate messages from agent execution with function calls
     messages = [
-        ChatMessage(role="user", contents=[{"type": "text", "text": "What's the weather in SF?"}]),
-        ChatMessage(
+        Message(role="user", contents=[{"type": "text", "text": "What's the weather in SF?"}]),
+        Message(
             role="assistant",
             contents=[
                 {
@@ -228,7 +228,7 @@ async def test_list_items_converts_function_calls():
                 }
             ],
         ),
-        ChatMessage(
+        Message(
             role="tool",
             contents=[
                 {
@@ -238,7 +238,7 @@ async def test_list_items_converts_function_calls():
                 }
             ],
         ),
-        ChatMessage(role="assistant", contents=[{"type": "text", "text": "The weather is sunny, 65°F"}]),
+        Message(role="assistant", contents=[{"type": "text", "text": "The weather is sunny, 65°F"}]),
     ]
 
     # Add messages to thread
@@ -284,7 +284,7 @@ async def test_list_items_converts_function_calls():
 @pytest.mark.asyncio
 async def test_list_items_handles_images_and_files():
     """Test that list_items properly converts data content (images/files) to OpenAI types."""
-    from agent_framework import ChatMessage, ChatMessageStore
+    from agent_framework import ChatMessageStore, Message
 
     store = InMemoryConversationStore()
 
@@ -300,7 +300,7 @@ async def test_list_items_handles_images_and_files():
 
     # Simulate message with image and file
     messages = [
-        ChatMessage(
+        Message(
             role="user",
             contents=[
                 {"type": "text", "text": "Check this image and PDF"},