Fix early-bird price blending and mislabeling; add contact-only events

- Early-bird pricing: RegistrationOption now tracks each purchase as a
  separate price tranche instead of overwriting a single price/quantity
  on repeat purchases, so buying more tickets after a tier expires no
  longer re-prices tickets already bought at the old price. Stock-limit
  checks, total-due calculation, and the Finance report's revenue-by-
  option are all tranche-aware; pages that showed one blended price per
  line now render/total each tranche. Viewing a pending/partially-paid
  registration (dashboard, detail page, or an event's registration
  list) now refreshes stale pricing on the spot instead of only at
  payment time.
- Fixed the "(early bird)" dashboard label incorrectly firing on any
  line priced below the base option price (e.g. a plain cheaper
  variant) — it now checks the real applied-tier flag.
- Added contact-only events (e.g. baptism): no registration/payment
  flow, shown on the public site with a "Contact us" popup instead of
  a Register button. Configurable via the admin event wizard.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/app/dashboard/supervisor/payments/page.tsx

@@ -199,8 +199,9 @@ function PaymentsContent() {
       const now = new Date();
       const map: Record<string, { totalDue: number; totalPaid: number; outstanding: number }> = {};
       for (const r of list) {
-        // totalDue uses priceSnapshot — not time-dependent
-        const totalDue = (r.registrationOptions || []).reduce((sum: number, opt: any) => sum + optionUnitPrice(opt, null, now) * (opt.quantity || 0), 0);
+        // Backend attaches a tranche-aware totalDueComputed (exact even when a line spans
+        // multiple early-bird prices) — fall back to the old client-side estimate otherwise.
+        const totalDue = r.totalDueComputed ?? (r.registrationOptions || []).reduce((sum: number, opt: any) => sum + optionUnitPrice(opt, null, now) * (opt.quantity || 0), 0);
         const totalPaid = (r.payments || []).reduce((s: number, p: any) => s + (p.amount || 0), 0);
         map[r.id] = { totalDue, totalPaid, outstanding: Math.max(0, totalDue - totalPaid) };
       }