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/playwright.config.ts

@@ -0,0 +1,35 @@
+import { defineConfig, devices } from "@playwright/test";
+import * as dotenv from "dotenv";
+import * as path from "path";
+
+dotenv.config({ path: path.resolve(__dirname, ".env") });
+
+export default defineConfig({
+  testDir: "./tests",
+  fullyParallel: false,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 1 : 0,
+  workers: 1,
+  reporter: "list",
+
+  // LLMs son lentos — timeouts generosos
+  timeout: 60_000,
+  expect: { timeout: 30_000 },
+
+  use: {
+    baseURL: process.env.ELEMENT_URL || "http://localhost:8080",
+    headless: true,
+    screenshot: "only-on-failure",
+    trace: "on-first-retry",
+    actionTimeout: 30_000,
+  },
+
+  globalSetup: "./global-setup.ts",
+
+  projects: [
+    {
+      name: "chromium",
+      use: { ...devices["Desktop Chrome"] },
+    },
+  ],
+});