test(e2e): setup Playwright with login smoke test

- Installed @playwright/test + Chromium
- playwright.config.js: baseURL localhost:5001, Desktop Chrome
- tests/e2e/login.spec.js: validates login form loads and invalid
  credentials show error

playwright.config.js

@@ -0,0 +1,21 @@
+const { defineConfig, devices } = require('@playwright/test');
+
+module.exports = defineConfig({
+  testDir: './tests/e2e',
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: 'list',
+  use: {
+    baseURL: 'http://localhost:5001',
+    trace: 'on-first-retry',
+    screenshot: 'only-on-failure',
+  },
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+});