build(web): add project-local Playwright tooling

- build: pin Playwright Test and MCP with repository-local npm, browser, and artifact paths plus sandboxed headless Chromium configuration.
- test: add a browser smoke test for the login page while keeping Playwright isolated from Vitest.
- docs: document Debian dependency setup, dual Chromium revisions, E2E commands, and project-scoped Codex MCP usage.

web/e2e/login-page.spec.ts

@@ -0,0 +1,11 @@
+import { expect, test } from '@playwright/test'
+
+test('renders the login page in a real browser', async ({ page }) => {
+  const response = await page.goto('/login')
+
+  expect(response?.ok()).toBe(true)
+  await expect(page.getByRole('heading', { name: 'Sign in to MyGO' })).toBeVisible()
+  await expect(page.getByLabel('Email')).toBeVisible()
+  await expect(page.getByLabel('Password')).toBeVisible()
+  await expect(page.getByRole('button', { name: 'Sign in' })).toBeVisible()
+})