feat(fase2): add Flow models, Flow Engine setup, update Docker Compose

- Add Flow and FlowSession SQLAlchemy models for chatbot flows
- Add TriggerType enum (welcome, keyword, fallback, event, manual)
- Setup flow-engine service with FastAPI structure
- Add flow-engine to docker-compose.yml

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

services/flow-engine/Dockerfile

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+FROM python:3.11-slim
+
+WORKDIR /app
+
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc \
+    libpq-dev \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY app ./app
+
+EXPOSE 8001
+
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8001"]

services/flow-engine/app/__init__.py

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+# WhatsApp Centralizado - Flow Engine

services/flow-engine/app/config.py

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+from pydantic_settings import BaseSettings
+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"
+    API_GATEWAY_URL: str = "http://localhost:8000"
+    WHATSAPP_CORE_URL: str = "http://localhost:3001"
+
+    class Config:
+        env_file = ".env"
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()

services/flow-engine/requirements.txt

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+fastapi==0.115.6
+uvicorn[standard]==0.34.0
+sqlalchemy==2.0.36
+psycopg2-binary==2.9.10
+redis==5.2.1
+httpx==0.28.1
+pydantic==2.10.4
+pydantic-settings==2.7.1