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/getting_started/context_providers/redis/redis_basics.py

@@ -30,7 +30,7 @@ Run:
 import asyncio
 import os
 
-from agent_framework import ChatMessage, tool
+from agent_framework import Message, tool
 from agent_framework.openai import OpenAIChatClient
 from agent_framework_redis._provider import RedisProvider
 from redisvl.extensions.cache.embeddings import EmbeddingsCache
@@ -128,9 +128,9 @@ async def main() -> None:
 
     # Build sample chat messages to persist to Redis
     messages = [
-        ChatMessage("user", ["runA CONVO: User Message"]),
-        ChatMessage("assistant", ["runA CONVO: Assistant Message"]),
-        ChatMessage("system", ["runA CONVO: System Message"]),
+        Message("user", ["runA CONVO: User Message"]),
+        Message("assistant", ["runA CONVO: Assistant Message"]),
+        Message("system", ["runA CONVO: System Message"]),
     ]
 
     # Declare/start a conversation/thread and write messages under 'runA'.
@@ -142,7 +142,7 @@ async def main() -> None:
     # Retrieve relevant memories for a hypothetical model call. The provider uses
     # the current request messages as the retrieval query and returns context to
     # be injected into the model's instructions.
-    ctx = await provider.invoking([ChatMessage("system", ["B: Assistant Message"])])
+    ctx = await provider.invoking([Message("system", ["B: Assistant Message"])])
 
     # Inspect retrieved memories that would be injected into instructions
     # (Debug-only output so you can verify retrieval works as expected.)