feat: complete fases 3,4,5 - frontend, containers, e2e tests

FASE 3 - Frontend (22 paginas):
- Leads (listado, detalle, nuevo), Cotizaciones, Arqueo
- Cursos, Alumnos, Empresas (listado, detalle, ventas)
- Reportes (ventas, ventas-empresas, reimpresion)
- Autorizador, Contacto

FASE 4 - Contenedores:
- docker-compose.yml (backend-api + services-externos + frontend)
- Dockerfiles para backend, services-externos, frontend
- .env.example con secretos

FASE 5 - Pruebas E2E:
- Playwright config + 3 spec files (login, leads, dashboard)
- 7 escenarios: login, error, sidebar, crear lead,
  dashboard cards, timeout, reportes

docker-compose.yml

@@ -0,0 +1,51 @@
+version: '3.8'
+services:
+  backend-api:
+    build:
+      context: ./backend
+      dockerfile: src/Ventas.API/Dockerfile
+    environment:
+      - ConnectionStrings__Default=Host=192.168.0.254;Port=5432;Database=ichn;Username=postgres;Password=apoca11
+      - Jwt__Secret=${JWT_SECRET}
+      - Jwt__Expiration=30
+    ports:
+      - "5000:8080"
+    networks:
+      - ventas-network
+    extra_hosts:
+      - "host.docker.internal:192.168.0.254"
+
+  services-externos:
+    build:
+      context: ./services-externos
+      dockerfile: src/ServicesExternos.API/Dockerfile
+    environment:
+      - LibreDTE__UserHash=${LIBREDTE_USER_HASH}
+      - LibreDTE__Ambiente=${LIBREDTE_AMBIENTE:-1}
+      - Transbank__ApiKey=${TRANSBANK_API_KEY}
+      - Transbank__CommerceCode=${TRANSBANK_COMMERCE_CODE}
+      - Transbank__Environment=${TRANSBANK_ENVIRONMENT:-integration}
+      - Email__Host=smtp.gmail.com
+      - Email__Port=587
+      - Email__User=noresponder@norteamericano.cl
+      - Email__Password=${SMTP_PASSWORD}
+    ports:
+      - "5001:8080"
+    networks:
+      - ventas-network
+
+  frontend:
+    build: ./frontend
+    environment:
+      - NEXT_PUBLIC_API_URL=http://backend-api:8080/api
+      - NEXT_PUBLIC_SERVICES_URL=http://services-externos:8080/api
+    ports:
+      - "3000:3000"
+    depends_on:
+      - backend-api
+    networks:
+      - ventas-network
+
+networks:
+  ventas-network:
+    driver: bridge