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/src/views/EventCreateView.vue

@@ -184,6 +184,7 @@ async function handleSubmit() {
         title: form.title.trim(),
         description: form.description.trim() || undefined,
         dateTime: dateTimeWithOffset,
+        timezone: Intl.DateTimeFormat().resolvedOptions().timeZone,
         location: form.location.trim() || undefined,
         expiryDate: form.expiryDate,
       },