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/sequential_agents.py

@@ -3,7 +3,7 @@
 import asyncio
 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
@@ -12,7 +12,7 @@ from azure.identity import AzureCliCredential
 Sample: Sequential workflow (agent-focused API) with shared conversation context
 
 Build a high-level sequential workflow using SequentialBuilder and two domain agents.
-The shared conversation (list[ChatMessage]) flows through each participant. Each agent
+The shared conversation (list[Message]) flows through each participant. Each agent
 appends its assistant message to the context. The workflow outputs the final conversation
 list when complete.
 
@@ -30,14 +30,14 @@ Prerequisites:
 
 async def main() -> None:
     # 1) Create agents
-    chat_client = AzureOpenAIChatClient(credential=AzureCliCredential())
+    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",
     )
@@ -46,10 +46,10 @@ async def main() -> None:
     workflow = SequentialBuilder(participants=[writer, reviewer]).build()
 
     # 3) Run and collect outputs
-    outputs: list[list[ChatMessage]] = []
+    outputs: list[list[Message]] = []
     async for event in workflow.run("Write a tagline for a budget-friendly eBike.", stream=True):
         if event.type == "output":
-            outputs.append(cast(list[ChatMessage], event.data))
+            outputs.append(cast(list[Message], event.data))
 
     if outputs:
         print("===== Final Conversation =====")