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/semantic-kernel-migration/orchestrations/sequential.py

@@ -15,7 +15,7 @@ import asyncio
 from collections.abc import Sequence
 from typing import cast
 
-from agent_framework import ChatMessage
+from agent_framework import Message
 from agent_framework.azure import AzureOpenAIChatClient
 from agent_framework.orchestrations import SequentialBuilder
 from azure.identity import AzureCliCredential
@@ -70,25 +70,25 @@ async def sk_agent_response_callback(
 ######################################################################
 
 
-async def run_agent_framework_example(prompt: str) -> list[ChatMessage]:
-    chat_client = AzureOpenAIChatClient(credential=AzureCliCredential())
+async def run_agent_framework_example(prompt: str) -> list[Message]:
+    client = AzureOpenAIChatClient(credential=AzureCliCredential())
 
-    writer = chat_client.as_agent(
+    writer = client.as_agent(
         instructions=("You are a concise copywriter. Provide a single, punchy marketing sentence based on the prompt."),
         name="writer",
     )
 
-    reviewer = chat_client.as_agent(
+    reviewer = client.as_agent(
         instructions=("You are a thoughtful reviewer. Give brief feedback on the previous assistant message."),
         name="reviewer",
     )
 
     workflow = SequentialBuilder(participants=[writer, reviewer]).build()
 
-    conversation_outputs: list[list[ChatMessage]] = []
+    conversation_outputs: list[list[Message]] = []
     async for event in workflow.run(prompt, stream=True):
         if event.type == "output":
-            conversation_outputs.append(cast(list[ChatMessage], event.data))
+            conversation_outputs.append(cast(list[Message], event.data))
 
     return conversation_outputs[-1] if conversation_outputs else []
 
@@ -112,7 +112,7 @@ async def run_semantic_kernel_example(prompt: str) -> str:
         await runtime.stop_when_idle()
 
 
-def _format_conversation(conversation: list[ChatMessage]) -> None:
+def _format_conversation(conversation: list[Message]) -> None:
     if not conversation:
         print("No Agent Framework output.")
         return