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/checklists/requirements.md

@@ -0,0 +1,35 @@
+# Specification Quality Checklist: Watch Event
+
+**Purpose**: Validate specification completeness and quality before proceeding to planning
+**Created**: 2026-03-12
+**Feature**: [spec.md](../spec.md)
+
+## Content Quality
+
+- [x] No implementation details (languages, frameworks, APIs)
+- [x] Focused on user value and business needs
+- [x] Written for non-technical stakeholders
+- [x] All mandatory sections completed
+
+## Requirement Completeness
+
+- [x] No [NEEDS CLARIFICATION] markers remain
+- [x] Requirements are testable and unambiguous
+- [x] Success criteria are measurable
+- [x] Success criteria are technology-agnostic (no implementation details)
+- [x] All acceptance scenarios are defined
+- [x] Edge cases are identified
+- [x] Scope is clearly bounded
+- [x] Dependencies and assumptions identified
+
+## Feature Readiness
+
+- [x] All functional requirements have clear acceptance criteria
+- [x] User scenarios cover primary flows
+- [x] Feature meets measurable outcomes defined in Success Criteria
+- [x] No implementation details leak into specification
+
+## Notes
+
+- All items pass. Spec is ready for `/speckit.clarify` or `/speckit.plan`.
+- localStorage is mentioned as a storage mechanism — this is an existing project convention (not an implementation detail introduced by this spec).