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/demos/hosted_agents/agent_with_text_search_rag/main.py

@@ -6,7 +6,7 @@ from collections.abc import MutableSequence
 from dataclasses import dataclass
 from typing import Any
 
-from agent_framework import ChatMessage, Context, ContextProvider
+from agent_framework import Context, ContextProvider, Message
 from agent_framework.azure import AzureOpenAIChatClient
 from azure.ai.agentserver.agentframework import from_agent_framework  # pyright: ignore[reportUnknownVariableType]
 from azure.identity import DefaultAzureCredential
@@ -27,16 +27,16 @@ class TextSearchResult:
 class TextSearchContextProvider(ContextProvider):
     """A simple context provider that simulates text search results based on keywords in the user's message."""
 
-    def _get_most_recent_message(self, messages: ChatMessage | MutableSequence[ChatMessage]) -> ChatMessage:
+    def _get_most_recent_message(self, messages: Message | MutableSequence[Message]) -> Message:
         """Helper method to extract the most recent message from the input."""
-        if isinstance(messages, ChatMessage):
+        if isinstance(messages, Message):
             return messages
         if messages:
             return messages[-1]
         raise ValueError("No messages provided")
 
     @override
-    async def invoking(self, messages: ChatMessage | MutableSequence[ChatMessage], **kwargs: Any) -> Context:
+    async def invoking(self, messages: Message | MutableSequence[Message], **kwargs: Any) -> Context:
         message = self._get_most_recent_message(messages)
         query = message.text.lower()
 
@@ -84,7 +84,7 @@ class TextSearchContextProvider(ContextProvider):
 
         return Context(
             messages=[
-                ChatMessage(
+                Message(
                     role="user", text="\n\n".join(json.dumps(result.__dict__, indent=2) for result in results)
                 )
             ]