Add bundle types: pick any, buy X get Y free, group discount

Bundles get a kind: exact (as before), mix (any setSize of the qualifying tickets for
a set price), free (cheapest freeCount in each set free) and group (setSize or more
qualifying tickets at a per-ticket price or % off, applied once). The supervisor page
has a type picker, buyers see a one-line description of each deal, and the Complete
bundle cards handle every type. Demo: Family Fun Day adds a Lunch for four deal.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/prisma/migrations/20261021141045_add_bundle_kinds/migration.sql

@@ -0,0 +1,12 @@
+-- CreateEnum
+CREATE TYPE "BundleKind" AS ENUM ('exact', 'mix', 'free', 'group');
+
+-- CreateEnum
+CREATE TYPE "BundleGroupPricing" AS ENUM ('per_ticket', 'percent');
+
+-- AlterTable
+ALTER TABLE "EventBundle" ADD COLUMN     "freeCount" INTEGER,
+ADD COLUMN     "groupPricing" "BundleGroupPricing",
+ADD COLUMN     "kind" "BundleKind" NOT NULL DEFAULT 'exact',
+ADD COLUMN     "setSize" INTEGER;
+

backend/prisma/schema.prisma

@@ -914,29 +914,52 @@ model CouponRedemption {
 
 // ─── Bundle deals ─────────────────────────────────────────────────────────────
 
-// A set of tickets sold together for one price, e.g. 5 Adult + 3 Child for R500.
-// Applied automatically, as many times as a registration's items allow, and only
-// when it beats what the items would cost anyway (see utils/bundles.js).
+// How a bundle is made up (see utils/bundles.js):
+// exact: these tickets in these numbers, for `price`, e.g. 5 Adult + 3 Child for R500
+// mix:   any `setSize` of the qualifying tickets, for `price`
+// free:  any `setSize` of the qualifying tickets, the cheapest `freeCount` free
+// group: `setSize` or more qualifying tickets, all at `price` each (or `price`% off)
+enum BundleKind {
+  exact
+  mix
+  free
+  group
+}
+
+enum BundleGroupPricing {
+  per_ticket
+  percent
+}
+
+// Tickets sold together at a better price. Applied automatically, as many times as a
+// registration's items allow (a group discount once), and only when it beats what the
+// items would cost anyway (see utils/bundles.js).
 model EventBundle {
-  id          String               @id @default(uuid())
-  eventId     String
-  name        String
-  description String?
-  price       Float
-  isActive    Boolean              @default(true)
-  validFrom   DateTime?
-  validUntil  DateTime?
-  order       Int                  @default(0)
-  createdAt   DateTime             @default(now())
-  updatedAt   DateTime             @updatedAt
-  event       Event                @relation(fields: [eventId], references: [id], onDelete: Cascade)
-  items       EventBundleItem[]
-  uses        RegistrationBundle[]
+  id           String               @id @default(uuid())
+  eventId      String
+  name         String
+  description  String?
+  kind         BundleKind           @default(exact)
+  // exact/mix: the set's price. group: the per-ticket price, or the percentage off.
+  price        Float
+  setSize      Int?
+  freeCount    Int?
+  groupPricing BundleGroupPricing?
+  isActive     Boolean              @default(true)
+  validFrom    DateTime?
+  validUntil   DateTime?
+  order        Int                  @default(0)
+  createdAt    DateTime             @default(now())
+  updatedAt    DateTime             @updatedAt
+  event        Event                @relation(fields: [eventId], references: [id], onDelete: Cascade)
+  items        EventBundleItem[]
+  uses         RegistrationBundle[]
 
   @@index([eventId])
 }
 
-// One line of a bundle. variantId null = any variant of the option.
+// One line of a bundle: for exact bundles a ticket and how many; for the others a
+// qualifying ticket (quantity unused). variantId null = any variant of the option.
 model EventBundleItem {
   id            String         @id @default(uuid())
   bundleId      String