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/router/index.ts

@@ -17,7 +17,7 @@ const router = createRouter({
     {
       path: '/events/:token',
       name: 'event',
-      component: () => import('../views/EventStubView.vue'),
+      component: () => import('../views/EventDetailView.vue'),
     },
   ],
 })