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/packages/declarative/tests/test_declarative_loader.py

@@ -483,7 +483,7 @@ class TestAgentFactoryCreateFromDict:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_dict(agent_def)
 
         assert agent is not None
@@ -512,7 +512,7 @@ instructions: You are a helpful assistant.
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
 
         # Create from YAML string
         agent_from_yaml = factory.create_agent_from_yaml(yaml_content)
@@ -540,7 +540,7 @@ instructions: You are a helpful assistant.
             factory.create_agent_from_dict(agent_def)
 
     def test_create_agent_from_dict_without_model_or_client_raises(self):
-        """Test that missing both model and chat_client raises DeclarativeLoaderError."""
+        """Test that missing both model and client raises DeclarativeLoaderError."""
         from agent_framework_declarative import AgentFactory
         from agent_framework_declarative._loader import DeclarativeLoaderError
 
@@ -592,7 +592,7 @@ instructions: Hello world
         monkeypatch.setenv("TEST_DESCRIPTION", "Description from env")
 
         # With safe_mode=True (default), Env access should fail and return original value
-        factory = AgentFactory(chat_client=mock_client, safe_mode=True)
+        factory = AgentFactory(client=mock_client, safe_mode=True)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # The description should NOT be resolved from env (PowerFx fails, returns original)
@@ -618,7 +618,7 @@ instructions: Hello world
 """
 
         # With safe_mode=False, Env access should work
-        factory = AgentFactory(chat_client=mock_client, safe_mode=False)
+        factory = AgentFactory(client=mock_client, safe_mode=False)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # The description should be resolved from env
@@ -726,7 +726,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools
@@ -761,7 +761,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools
@@ -800,7 +800,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools
@@ -836,7 +836,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools
@@ -868,7 +868,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools
@@ -907,7 +907,7 @@ tools:
         mock_client = MagicMock()
         mock_client.create_agent.return_value = MagicMock()
 
-        factory = AgentFactory(chat_client=mock_client)
+        factory = AgentFactory(client=mock_client)
         agent = factory.create_agent_from_yaml(yaml_content)
 
         # Find the MCP tool in the agent's tools