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>

specs/018-cancel-event-list/plan.md

@@ -0,0 +1,69 @@
+# Implementation Plan: Cancel Event from Event List
+
+**Branch**: `018-cancel-event-list` | **Date**: 2026-03-12 | **Spec**: [spec.md](spec.md)
+**Input**: Feature specification from `/specs/018-cancel-event-list/spec.md`
+
+## Summary
+
+Enable organizers to cancel events directly from the event list page via the existing ConfirmDialog. The `EventList.vue` `confirmDelete` handler must detect the organizer role and call `PATCH /events/{eventToken}?organizerToken=...` with `{ cancelled: true }` instead of the existing RSVP deletion flow. The ConfirmDialog message must differentiate organizer cancellation (severe, affects all attendees) from attendee RSVP cancellation.
+
+## Technical Context
+
+**Language/Version**: TypeScript 5.x, Vue 3 (Composition API)
+**Primary Dependencies**: openapi-fetch, Vue Router, Vite
+**Storage**: localStorage via `useEventStorage()` composable
+**Testing**: Vitest (unit), Playwright + MSW (E2E)
+**Target Platform**: Mobile-first PWA (all modern browsers)
+**Project Type**: Web application (frontend-only change)
+**Performance Goals**: N/A (no new endpoints, minimal UI change)
+**Constraints**: No backend changes required; cancel-event API already exists
+**Scale/Scope**: ~50 lines of logic change in EventList.vue, dialog message updates
+
+## Constitution Check
+
+*GATE: Must pass before Phase 0 research. Re-check after Phase 1 design.*
+
+| Principle | Status | Notes |
+|-----------|--------|-------|
+| I. Privacy by Design | PASS | No new data collected or stored |
+| II. Test-Driven Methodology | PASS | Unit tests + E2E tests planned |
+| III. API-First Development | PASS | Uses existing PATCH endpoint already in OpenAPI spec |
+| IV. Simplicity & Quality | PASS | Extends existing delete flow, no new abstractions |
+| V. Dependency Discipline | PASS | No new dependencies |
+| VI. Accessibility | PASS | Reuses existing ConfirmDialog (already has aria-modal, alertdialog role, keyboard nav) |
+
+All gates pass. No violations.
+
+## Project Structure
+
+### Documentation (this feature)
+
+```text
+specs/018-cancel-event-list/
+├── plan.md              # This file
+├── research.md          # Phase 0 output
+├── data-model.md        # Phase 1 output (minimal — no new entities)
+└── tasks.md             # Phase 2 output (/speckit.tasks command)
+```
+
+### Source Code (repository root)
+
+```text
+frontend/src/
+├── components/
+│   ├── EventList.vue         # PRIMARY CHANGE: confirmDelete handler + dialog message
+│   └── ConfirmDialog.vue     # No changes needed
+├── api/
+│   ├── client.ts             # No changes needed (openapi-fetch client)
+│   └── schema.d.ts           # Already has PATCH /events/{eventToken} types
+└── composables/
+    └── useEventStorage.ts    # No changes needed
+
+frontend/e2e/
+└── cancel-event-list.spec.ts # NEW: E2E tests for organizer cancellation
+
+frontend/src/components/__tests__/
+└── EventList.spec.ts         # EXTEND: Unit tests for organizer cancel flow
+```
+
+**Structure Decision**: Frontend-only change. All logic changes in `EventList.vue`. No new components, composables, or API endpoints.