chore(visual): Phase 4 audit polish on event/series surface

Migrates event/series UI from Tailwind/Nuxt UI form components to the
zine pattern (dashed borders, CSS-var palette, native inputs). Restructures
single-event and series detail/index pages to the two-column grid pattern
matching about.vue and member/dashboard.vue.

Touches:
- app/components/EventSeriesTicketCard.vue — phantom-palette → CSS-var
  migration (--candle, --ember, --surface), color="gray" → "neutral"
- app/components/EventTicketCard.vue — --candle-faint border var
- app/components/EventTicketPurchase.vue — accent-color: var(--candle)
- app/pages/events/[slug].vue — page-fill flex chain, .event-body grid
- app/pages/events/index.vue — series link uses series.id (was _id)
- app/pages/series/[id].vue — two-column layout (1fr/280px) + sidebar
- app/pages/series/index.vue — full rewrite to dashed-border zine pattern

Per docs/specs/events-visual-audit-findings.md Phase 4. Behavior unchanged.

app/components/EventTicketPurchase.vue

@@ -463,6 +463,7 @@ const formatEventDate = (date) => {
 .consent-field input[type="checkbox"] {
   margin-top: 3px;
   flex-shrink: 0;
+  accent-color: var(--candle);
 }
 .consent-hint {
   margin-bottom: 14px;