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>

specs/017-watch-event/quickstart.md

@@ -0,0 +1,33 @@
+# Quickstart: Watch Event
+
+**Feature**: 017-watch-event
+**Date**: 2026-03-12
+
+## What This Feature Does
+
+Adds a bookmark icon to the event detail page that lets users save events locally without RSVPing. Saved events appear in the event list with a "Watching" label.
+
+## Files to Modify
+
+| File | Change |
+|------|--------|
+| `frontend/src/composables/useEventStorage.ts` | Add `saveWatch()` and `isStored()` methods |
+| `frontend/src/views/EventDetailView.vue` | Add bookmark icon left of title, shake animation trigger |
+| `frontend/src/components/EventList.vue` | Update `getRole()` to return `'watcher'`, skip confirmation for watchers |
+| `frontend/src/components/EventCard.vue` | Add `'watcher'` to role type, add badge styling |
+
+## Implementation Order
+
+1. **useEventStorage** — Add `saveWatch()` and `isStored()` (unit tests first)
+2. **EventCard** — Extend role type, add "Watching" badge with styling (unit tests first)
+3. **EventList** — Update `getRole()`, adjust delete flow for watchers (unit tests first)
+4. **EventDetailView** — Add bookmark icon with all states and shake animation
+5. **E2E tests** — Cover all 7 user stories from spec
+
+## Key Design Decisions
+
+- **No new StoredEvent fields** — watcher state is the absence of both `organizerToken` and `rsvpToken`
+- **No backend changes** — entirely client-side
+- **Bookmark icon left of title** — flex container, vertically centered
+- **Non-interactive for attendees/organizers** — tapping shakes the relevant bottom action button
+- **No confirmation dialog for watcher deletion** from event list