feat(fase4): add AI response and sentiment nodes

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

services/flow-engine/app/config.py

@@ -5,6 +5,11 @@ from functools import lru_cache
 class Settings(BaseSettings):
     DATABASE_URL: str = "postgresql://whatsapp_admin:password@localhost:5432/whatsapp_central"
     REDIS_URL: str = "redis://localhost:6379"
+
+    # OpenAI
+    OPENAI_API_KEY: str = ""
+    OPENAI_MODEL: str = "gpt-3.5-turbo"
+
     API_GATEWAY_URL: str = "http://localhost:8000"
     WHATSAPP_CORE_URL: str = "http://localhost:3001"