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/orchestrations/concurrent_agents.py

@@ -3,7 +3,7 @@
 import asyncio
 from typing import Any
 
-from agent_framework import ChatMessage
+from agent_framework import Message
 from agent_framework.azure import AzureOpenAIChatClient
 from agent_framework.orchestrations import ConcurrentBuilder
 from azure.identity import AzureCliCredential
@@ -14,7 +14,7 @@ Sample: Concurrent fan-out/fan-in (agent-only API) with default aggregator
 Build a high-level concurrent workflow using ConcurrentBuilder and three domain agents.
 The default dispatcher fans out the same user prompt to all agents in parallel.
 The default aggregator fans in their results and yields output containing
-a list[ChatMessage] representing the concatenated conversations from all agents.
+a list[Message] representing the concatenated conversations from all agents.
 
 Demonstrates:
 - Minimal wiring with ConcurrentBuilder(participants=[...]).build()
@@ -29,9 +29,9 @@ Prerequisites:
 
 async def main() -> None:
     # 1) Create three domain agents using AzureOpenAIChatClient
-    chat_client = AzureOpenAIChatClient(credential=AzureCliCredential())
+    client = AzureOpenAIChatClient(credential=AzureCliCredential())
 
-    researcher = chat_client.as_agent(
+    researcher = client.as_agent(
         instructions=(
             "You're an expert market and product researcher. Given a prompt, provide concise, factual insights,"
             " opportunities, and risks."
@@ -39,7 +39,7 @@ async def main() -> None:
         name="researcher",
     )
 
-    marketer = chat_client.as_agent(
+    marketer = client.as_agent(
         instructions=(
             "You're a creative marketing strategist. Craft compelling value propositions and target messaging"
             " aligned to the prompt."
@@ -47,7 +47,7 @@ async def main() -> None:
         name="marketer",
     )
 
-    legal = chat_client.as_agent(
+    legal = client.as_agent(
         instructions=(
             "You're a cautious legal/compliance reviewer. Highlight constraints, disclaimers, and policy concerns"
             " based on the prompt."
@@ -66,7 +66,7 @@ async def main() -> None:
     if outputs:
         print("===== Final Aggregated Conversation (messages) =====")
         for output in outputs:
-            messages: list[ChatMessage] | Any = output
+            messages: list[Message] | Any = output
             for i, msg in enumerate(messages, start=1):
                 name = msg.author_name if msg.author_name else "user"
                 print(f"{'-' * 60}\n\n{i:02d} [{name}]:\n{msg.text}")