feat(phase2): integrate flow engine and add flows navigation

- Add FLOW_ENGINE_URL to API Gateway config
- Integrate flow engine in message handler (BOT status only)
- Add /flows routes to MainLayout with FlowList and FlowBuilder
- Add Flujos menu item with ApartmentOutlined icon

This completes Phase 2: Flow Engine Básico

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

services/api-gateway/app/routers/whatsapp.py

@@ -271,6 +271,38 @@ async def handle_whatsapp_event(
 
         from datetime import datetime
         conversation.last_message_at = datetime.utcnow()
+        db.commit()
+        db.refresh(message)
+
+        # Process message through Flow Engine (if in BOT status)
+        if conversation.status == ConversationStatus.BOT:
+            async with httpx.AsyncClient() as client:
+                try:
+                    await client.post(
+                        f"{settings.FLOW_ENGINE_URL}/process",
+                        json={
+                            "conversation_id": str(conversation.id),
+                            "contact": {
+                                "id": str(contact.id),
+                                "phone_number": contact.phone_number,
+                                "name": contact.name,
+                            },
+                            "conversation": {
+                                "id": str(conversation.id),
+                                "status": conversation.status.value,
+                            },
+                            "message": {
+                                "id": str(message.id),
+                                "content": content,
+                                "type": message.type.value,
+                            },
+                        },
+                        timeout=30,
+                    )
+                except Exception as e:
+                    print(f"Flow engine error: {e}")
+
+        return {"status": "ok"}
 
     db.commit()
     return {"status": "ok"}