Add Playwright E2E tests with MSW API mocking

- Playwright + @msw/playwright + @msw/source for OpenAPI-driven mocks
- Chromium-only configuration with Vite dev server integration
- Smoke tests: home page, CTA, navigation
- US-1 tests: validation, event creation flow, localStorage, error handling
- Suppress Node 25 --localstorage-file warning from MSW cookieStore

frontend/e2e/smoke.spec.ts

@@ -0,0 +1,20 @@
+import { test, expect } from './msw-setup'
+
+test.describe('Smoke', () => {
+  test('home page loads and shows branding', async ({ page }) => {
+    await page.goto('/')
+    await expect(page.getByRole('heading', { name: 'fete' })).toBeVisible()
+  })
+
+  test('home page has create event CTA', async ({ page }) => {
+    await page.goto('/')
+    await expect(page.getByRole('link', { name: /create event/i })).toBeVisible()
+  })
+
+  test('navigating to /create shows the creation form', async ({ page }) => {
+    await page.goto('/')
+    await page.getByRole('link', { name: /create event/i }).click()
+    await expect(page).toHaveURL('/create')
+    await expect(page.getByLabel(/title/i)).toBeVisible()
+  })
+})