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/register/[eventId]/page.tsx

@@ -1,4 +1,4 @@
-import { notFound } from "next/navigation";
+import { notFound, redirect } from "next/navigation";
 import { Navbar } from "@/components/layout/Navbar";
 import { Footer } from "@/components/layout/Footer";
 import { apiFetch, ApiError } from "@/lib/api";
@@ -18,6 +18,12 @@ export default async function RegisterPage({ params }: { params: Promise<{ event
     throw e;
   }
 
+  // Contact-only events (e.g. baptism) have no registration flow — bounce a stale/direct
+  // link back to the event detail page, which renders the Contact affordance instead.
+  if (event.requiresRegistration === false) {
+    redirect(`/events/${eventId}`);
+  }
+
   return (
     <div className="min-h-screen flex flex-col">
       <Navbar />