feat(fase2): add Flow API routes and Flow Engine main app

API Gateway:
- Add flows router with CRUD endpoints
- Add activate/deactivate endpoints
- Auto-deactivate other flows for welcome/fallback triggers

Flow Engine:
- Add main.py with FastAPI app
- Add /process endpoint for message handling
- Add SQLAlchemy models (mirrors api-gateway)

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

services/api-gateway/app/main.py

@@ -2,7 +2,7 @@ from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 from app.core.config import get_settings
 from app.core.database import engine, Base
-from app.routers import auth, whatsapp
+from app.routers import auth, whatsapp, flows
 
 settings = get_settings()
 
@@ -28,6 +28,7 @@ app.add_middleware(
 # Routers
 app.include_router(auth.router)
 app.include_router(whatsapp.router)
+app.include_router(flows.router)
 
 
 @app.get("/health")