refactor: move estado da sessão para o domínio

tests/test_voice_pipeline.py

@@ -27,7 +27,7 @@ from voice_assistant.voice_pipeline import (
     VoicePipeline,
 )
 
-from voice_assistant.audio_gateway.app.session import SessionState
+from voice_assistant.domain.session import SessionState
 from voice_assistant.turn_manager import TurnManager, TurnState
 from voice_assistant.agent.mock import MockAgentAdapter
 from voice_assistant.tts.mock import MockTTSAdapter