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>

frontend/src/layouts/MainLayout.tsx

@@ -10,11 +10,14 @@ import {
   UserOutlined,
   MenuFoldOutlined,
   MenuUnfoldOutlined,
+  ApartmentOutlined,
 } from '@ant-design/icons';
 import { useAuthStore } from '../store/auth';
 import Dashboard from '../pages/Dashboard';
 import WhatsAppAccounts from '../pages/WhatsAppAccounts';
 import Inbox from '../pages/Inbox';
+import FlowList from '../pages/FlowList';
+import FlowBuilder from '../pages/FlowBuilder';
 
 const { Header, Sider, Content } = Layout;
 const { Text } = Typography;
@@ -46,6 +49,11 @@ export default function MainLayout() {
       icon: <WhatsAppOutlined />,
       label: 'WhatsApp',
     },
+    {
+      key: '/flows',
+      icon: <ApartmentOutlined />,
+      label: 'Flujos',
+    },
     {
       key: '/settings',
       icon: <SettingOutlined />,
@@ -151,6 +159,9 @@ export default function MainLayout() {
             <Route path="/" element={<Dashboard />} />
             <Route path="/inbox" element={<Inbox />} />
             <Route path="/whatsapp" element={<WhatsAppAccounts />} />
+            <Route path="/flows" element={<FlowList />} />
+            <Route path="/flows/new" element={<FlowBuilder />} />
+            <Route path="/flows/:id" element={<FlowBuilder />} />
             <Route path="/settings" element={<div>Configuración (próximamente)</div>} />
           </Routes>
         </Content>