AgentKit shutdown bypasses FeishuChannelExtension in-flight message draining #901

Description

AgentKit applications created with:

create_agentkit_app(root_agent, enable_feishu=True)

do not actually use the lifecycle implemented by FeishuChannelExtension. AgentKit currently maintains a separate background thread and reconnect loop that calls the underlying Feishu SDK Channel's start() and stop() methods directly.

As a result, FeishuChannelExtension.start() and FeishuChannelExtension.shutdown() are bypassed. During application shutdown, in-flight Feishu messages are not drained before the process exits.

Current Behaviour:

The following expected logs are absent:

GRACEFUL_TEST_TOOL_COMPLETED
Shutting down Feishu channel: closing WebSocket and draining 1 in-flight message(s)...
Feishu channel drained; shutdown complete.

And the user will not receive the final Feishu reply.