Add organizer cancel-event flow to EventList

Organizers can now cancel events directly from the event list via the
existing PATCH /events/{eventToken} API. The confirmation dialog shows
role-differentiated messaging: "Cancel event?" with a severity warning
for organizers vs. "Remove event?" for attendees. Responses 204, 409,
and 404 all result in successful removal from the local list.

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

frontend/src/components/EventList.vue

@@ -27,7 +27,7 @@
     </section>
     <ConfirmDialog
       :open="!!pendingDeleteToken"
-      title="Remove event?"
+      :title="deleteDialogTitle"
       :message="deleteDialogMessage"
       confirm-label="Remove"
       cancel-label="Cancel"
@@ -49,13 +49,26 @@ import DateSubheader from './DateSubheader.vue'
 import ConfirmDialog from './ConfirmDialog.vue'
 import type { StoredEvent } from '../composables/useEventStorage'
 
-const { getStoredEvents, getRsvp, removeEvent } = useEventStorage()
+const { getStoredEvents, getRsvp, getOrganizerToken, removeEvent } = useEventStorage()
 
 const pendingDeleteToken = ref<string | null>(null)
 const deleteError = ref('')
 
+const pendingDeleteRole = computed(() => {
+  if (!pendingDeleteToken.value) return null
+  const event = getStoredEvents().find((e) => e.eventToken === pendingDeleteToken.value)
+  return event ? getRole(event) : null
+})
+
+const deleteDialogTitle = computed(() => {
+  return pendingDeleteRole.value === 'organizer' ? 'Cancel event?' : 'Remove event?'
+})
+
 const deleteDialogMessage = computed(() => {
   if (!pendingDeleteToken.value) return ''
+  if (pendingDeleteRole.value === 'organizer') {
+    return 'This will permanently cancel the event for all attendees.'
+  }
   const rsvp = getRsvp(pendingDeleteToken.value)
   if (rsvp) {
     return 'This event will be removed from your list and your attendance will be cancelled.'
@@ -77,6 +90,32 @@ async function confirmDelete() {
   if (!pendingDeleteToken.value) return
 
   const eventToken = pendingDeleteToken.value
+  const organizerToken = getOrganizerToken(eventToken)
+
+  if (organizerToken) {
+    try {
+      const { response } = await api.PATCH('/events/{eventToken}', {
+        params: {
+          path: { eventToken },
+          query: { organizerToken },
+        },
+        body: { cancelled: true },
+      })
+
+      if (response.status !== 204 && response.status !== 409 && response.status !== 404) {
+        deleteError.value = 'Could not cancel event. Please try again.'
+        return
+      }
+    } catch {
+      deleteError.value = 'Could not cancel event. Please try again.'
+      return
+    }
+
+    removeEvent(eventToken)
+    pendingDeleteToken.value = null
+    return
+  }
+
   const rsvp = getRsvp(eventToken)
 
   if (rsvp) {