Add EventDetailView with loading, expired, not-found, and error states

New view fetches event via openapi-fetch, formats date/time with
Intl.DateTimeFormat. Skeleton shimmer during loading (CSS-only).
Create form now sends auto-detected timezone.
Unit tests for all five view states, E2E tests with MSW mocks.

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

frontend/e2e/event-create.spec.ts

@@ -12,7 +12,7 @@ test.describe('US-1: Create an event', () => {
     await expect(page.getByText('Expiry date is required.')).toBeVisible()
   })
 
-  test('creates an event and redirects to stub page', async ({ page }) => {
+  test('creates an event and redirects to event detail page', async ({ page }) => {
     await page.goto('/create')
 
     await page.getByLabel(/title/i).fill('Summer BBQ')
@@ -24,7 +24,6 @@ test.describe('US-1: Create an event', () => {
     await page.getByRole('button', { name: /create event/i }).click()
 
     await expect(page).toHaveURL(/\/events\/.+/)
-    await expect(page.getByText('Event created!')).toBeVisible()
   })
 
   test('stores event data in localStorage after creation', async ({ page }) => {