Implement watch-event feature (017) with bookmark in RsvpBar

Add client-side watch/bookmark functionality: users can save events to
localStorage without RSVPing via a bookmark button next to the "I'm attending"
CTA. Watched events appear in the event list with a "Watching" label.
Bookmark is only visible for visitors (not attendees or organizers).

Includes spec, plan, research, tasks, unit tests, and E2E tests.

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

frontend/src/views/EventDetailView.vue

@@ -35,21 +35,21 @@
 
         <dl class="detail__meta">
           <div class="detail__meta-item">
-            <dt class="detail__meta-icon glass" aria-label="Date and time">
+            <dt class="detail__meta-icon" aria-label="Date and time">
               <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><rect x="3" y="4" width="18" height="18" rx="2"/><line x1="16" y1="2" x2="16" y2="6"/><line x1="8" y1="2" x2="8" y2="6"/><line x1="3" y1="10" x2="21" y2="10"/></svg>
             </dt>
             <dd class="detail__meta-text">{{ formattedDateTime }}</dd>
           </div>
 
           <div v-if="event.location" class="detail__meta-item">
-            <dt class="detail__meta-icon glass" aria-label="Location">
+            <dt class="detail__meta-icon" aria-label="Location">
               <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M21 10c0 7-9 13-9 13s-9-6-9-13a9 9 0 0 1 18 0z"/><circle cx="12" cy="10" r="3"/></svg>
             </dt>
             <dd class="detail__meta-text">{{ event.location }}</dd>
           </div>
 
           <div class="detail__meta-item">
-            <dt class="detail__meta-icon glass" aria-label="Attendees">
+            <dt class="detail__meta-icon" aria-label="Attendees">
               <svg width="18" height="18" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M17 21v-2a4 4 0 0 0-4-4H5a4 4 0 0 0-4 4v2"/><circle cx="9" cy="7" r="4"/><path d="M23 21v-2a4 4 0 0 0-3-3.87"/><path d="M16 3.13a4 4 0 0 1 0 7.75"/></svg>
             </dt>
             <dd class="detail__meta-text">{{ event.attendeeCount }} going</dd>
@@ -120,8 +120,10 @@
     <RsvpBar
       v-if="state === 'loaded' && event && !isOrganizer && !event.cancelled"
       :has-rsvp="!!rsvpName"
+      :bookmarked="eventIsStored"
       @open="sheetOpen = true"
       @cancel="confirmCancelOpen = true"
+      @bookmark="handleBookmarkClick"
     />
 
     <!-- Cancel confirmation dialog -->
@@ -179,7 +181,7 @@ type GetEventResponse = components['schemas']['GetEventResponse']
 type State = 'loading' | 'loaded' | 'not-found' | 'error'
 
 const route = useRoute()
-const { saveRsvp, getRsvp, removeRsvp, getOrganizerToken } = useEventStorage()
+const { saveRsvp, getRsvp, removeRsvp, getOrganizerToken, saveWatch, isStored, removeEvent } = useEventStorage()
 
 const state = ref<State>('loading')
 const event = ref<GetEventResponse | null>(null)
@@ -202,6 +204,20 @@ const cancelReasonInput = ref('')
 const cancelEventError = ref('')
 const cancellingEvent = ref(false)
 
+const eventToken = computed(() => route.params.eventToken as string)
+
+const eventIsStored = computed(() => isStored(eventToken.value))
+
+function handleBookmarkClick() {
+  if (!event.value) return
+  if (isOrganizer.value || rsvpName.value) return
+  if (eventIsStored.value) {
+    removeEvent(eventToken.value)
+  } else {
+    saveWatch(eventToken.value, event.value.title, event.value.dateTime)
+  }
+}
+
 const formattedDateTime = computed(() => {
   if (!event.value) return ''
   const formatted = new Intl.DateTimeFormat(undefined, {
@@ -469,6 +485,10 @@ onMounted(fetchEvent)
   padding-top: 4rem;
 }
 
+.detail__meta-icon svg {
+  display: block;
+}
+
 /* Title */
 .detail__title {
   font-size: 2rem;
@@ -501,6 +521,11 @@ onMounted(fetchEvent)
   justify-content: center;
   border-radius: 10px;
   color: var(--color-text-on-gradient);
+  line-height: 0;
+  background: linear-gradient(135deg, var(--color-glass-strong) 0%, var(--color-glass-subtle) 100%);
+  border: 1px solid var(--color-glass-border);
+  backdrop-filter: blur(16px);
+  -webkit-backdrop-filter: blur(16px);
 }
 
 .detail__meta-text {