feat: infraestructura base para E2E tests con Playwright

Proyecto Node.js independiente en e2e/ con Playwright + Chromium headless.
Incluye setup-element.sh para descargar y servir Element Web localmente
(puerto 8090 por defecto, 8080 ocupado por Docker).
Scripts de instalacion y placeholder para ejecucion de tests.
Cierra issue 0022a.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

e2e/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "agents-e2e",
+  "version": "1.0.0",
+  "private": true,
+  "description": "E2E tests for agents_and_robots via Playwright + Element Web",
+  "scripts": {
+    "test": "npx playwright test",
+    "test:headed": "npx playwright test --headed",
+    "test:debug": "npx playwright test --debug"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.50.0",
+    "dotenv": "^16.4.7"
+  }
+}