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/evaluation/self_reflection/self_reflection.py

@@ -17,7 +17,7 @@ from typing import Any
 
 import openai
 import pandas as pd
-from agent_framework import ChatAgent, ChatMessage
+from agent_framework import Agent, Message
 from agent_framework.azure import AzureOpenAIChatClient
 from azure.ai.projects import AIProjectClient
 from azure.identity import AzureCliCredential
@@ -142,7 +142,7 @@ def run_eval(
 async def execute_query_with_self_reflection(
     *,
     client: openai.OpenAI,
-    agent: ChatAgent,
+    agent: Agent,
     eval_object: openai.types.EvalCreateResponse,
     full_user_query: str,
     context: str,
@@ -152,7 +152,7 @@ async def execute_query_with_self_reflection(
     Execute a query with self-reflection loop.
 
     Args:
-        agent: ChatAgent instance to use for generating responses
+        agent: Agent instance to use for generating responses
         full_user_query: Complete prompt including system prompt, user request, and context
         context: Context document for groundedness evaluation
         evaluator: Groundedness evaluator function
@@ -170,7 +170,7 @@ async def execute_query_with_self_reflection(
             - total_groundedness_eval_time: Time spent on evaluations (seconds)
             - total_end_to_end_time: Total execution time (seconds)
     """
-    messages = [ChatMessage("user", [full_user_query])]
+    messages = [Message("user", [full_user_query])]
 
     best_score = 0
     max_score = 5
@@ -223,14 +223,14 @@ async def execute_query_with_self_reflection(
             print(f"  → No improvement (score: {score}/{max_score}). Trying again...")
 
         # Add to conversation history
-        messages.append(ChatMessage("assistant", [agent_response]))
+        messages.append(Message("assistant", [agent_response]))
 
         # Request improvement
         reflection_prompt = (
             f"The groundedness score of your response is {score}/{max_score}. "
             f"Reflect on your answer and improve it to get the maximum score of {max_score} "
         )
-        messages.append(ChatMessage("user", [reflection_prompt]))
+        messages.append(Message("user", [reflection_prompt]))
 
     end_time = time.time()
     latency = end_time - start_time