Add event list feature (009-list-events)

Enable users to see all their saved events on the home screen, sorted
by date with upcoming events first. Key capabilities:

- EventCard with title, relative time display, and organizer/attendee
  role badge
- Sortable EventList with past-event visual distinction (faded style)
- Empty state when no events are stored
- Swipe-to-delete gesture with confirmation dialog
- Floating action button for quick event creation
- Rename router param :token → :eventToken across all views
- useRelativeTime composable (Intl.RelativeTimeFormat)
- useEventStorage: add validation, removeEvent(), reactive versioning
- Full E2E and unit test coverage for all new components

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

frontend/src/composables/useRelativeTime.ts

@@ -0,0 +1,23 @@
+const UNITS: [Intl.RelativeTimeFormatUnit, number][] = [
+  ['year', 365 * 24 * 60 * 60],
+  ['month', 30 * 24 * 60 * 60],
+  ['week', 7 * 24 * 60 * 60],
+  ['day', 24 * 60 * 60],
+  ['hour', 60 * 60],
+  ['minute', 60],
+  ['second', 1],
+]
+
+export function formatRelativeTime(dateTime: string, now: Date = new Date()): string {
+  const target = new Date(dateTime)
+  const diffSeconds = Math.round((target.getTime() - now.getTime()) / 1000)
+
+  for (const [unit, secondsInUnit] of UNITS) {
+    if (Math.abs(diffSeconds) >= secondsInUnit) {
+      const value = Math.round(diffSeconds / secondsInUnit)
+      return new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' }).format(value, unit)
+    }
+  }
+
+  return new Intl.RelativeTimeFormat(undefined, { numeric: 'auto' }).format(0, 'second')
+}