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

tests/playwright.config.ts

@@ -0,0 +1,15 @@
+import { defineConfig } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './e2e',
+  timeout: 30000,
+  retries: 1,
+  use: {
+    baseURL: 'http://localhost:3000',
+    headless: true,
+    viewport: { width: 1280, height: 720 },
+  },
+  projects: [
+    { name: 'chromium', use: { browserName: 'chromium' } },
+  ],
+});