Add ticket transfer

Payers and holders can hand a ticket to someone else before the event.
The new holder gets a new QR code (and an inactive account with an
activation link if they're new); the old code stops working and scans
of it, online or in offline sync, say it was transferred. One place can
be split off a shared group ticket. Transfers can be turned off per
event (supervisors can always transfer from At the door), youth events
need the new holder's own consent, and every transfer is audited.

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

backend/prisma/migrations/20261019140949_add_ticket_transfer/migration.sql

@@ -0,0 +1,36 @@
+-- AlterEnum
+ALTER TYPE "AdminAuditAction" ADD VALUE 'ticket_transferred';
+
+-- AlterTable
+ALTER TABLE "Event" ADD COLUMN     "allowTicketTransfer" BOOLEAN NOT NULL DEFAULT true;
+
+-- CreateTable
+CREATE TABLE "TicketTransfer" (
+    "id" TEXT NOT NULL,
+    "ticketId" TEXT NOT NULL,
+    "fromHolderName" TEXT NOT NULL,
+    "fromUserId" TEXT,
+    "toName" TEXT NOT NULL,
+    "toUserId" TEXT,
+    "byUserId" TEXT,
+    "oldQrCode" TEXT,
+    "createdAt" TIMESTAMP(3) NOT NULL DEFAULT CURRENT_TIMESTAMP,
+
+    CONSTRAINT "TicketTransfer_pkey" PRIMARY KEY ("id")
+);
+
+-- CreateIndex
+CREATE INDEX "TicketTransfer_ticketId_idx" ON "TicketTransfer"("ticketId");
+
+-- CreateIndex
+CREATE INDEX "TicketTransfer_oldQrCode_idx" ON "TicketTransfer"("oldQrCode");
+
+-- AddForeignKey
+ALTER TABLE "TicketTransfer" ADD CONSTRAINT "TicketTransfer_ticketId_fkey" FOREIGN KEY ("ticketId") REFERENCES "Ticket"("id") ON DELETE CASCADE ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "TicketTransfer" ADD CONSTRAINT "TicketTransfer_toUserId_fkey" FOREIGN KEY ("toUserId") REFERENCES "User"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+
+-- AddForeignKey
+ALTER TABLE "TicketTransfer" ADD CONSTRAINT "TicketTransfer_byUserId_fkey" FOREIGN KEY ("byUserId") REFERENCES "User"("id") ON DELETE SET NULL ON UPDATE CASCADE;
+

backend/prisma/schema.prisma

@@ -106,6 +106,8 @@ model User {
   heldTickets      Ticket[]            @relation("TicketHolder")
   waitlistEntries  WaitlistEntry[]
   scanLocks        ScanLock[]          @relation("ScanLockOwner")
+  transfersTo      TicketTransfer[]    @relation("TransferRecipient")
+  transfersBy      TicketTransfer[]    @relation("TransferActor")
   scanLocksForced  ScanLock[]          @relation("ScanLockForcedBy")
   syncReportsDone  OfflineSyncReport[] @relation("SyncReportReviewer")
 
@@ -141,6 +143,7 @@ model Event {
   // them for waitlistOfferHours. waitlistPartialOffers: offer what's free even if it's
   // fewer places than asked for (otherwise skip to the next person who fits).
   waitlistEnabled         Boolean           @default(false)
+  allowTicketTransfer     Boolean           @default(true)
   waitlistOfferHours      Int               @default(24)
   waitlistPartialOffers   Boolean           @default(true)
   contactName             String?
@@ -365,6 +368,7 @@ model Ticket {
   user                 User               @relation(fields: [userId], references: [id], onDelete: Restrict)
   event                Event              @relation(fields: [eventId], references: [id], onDelete: Restrict)
   usages               TicketUsage[]
+  transfers            TicketTransfer[]
 
   @@index([holderUserId])
   @@index([eventId])
@@ -476,6 +480,7 @@ enum AdminAuditAction {
   scan_lock_released
   scan_lock_force_released
   offline_sync
+  ticket_transferred
 }
 
 // Append-only audit trail for admin/supervisor-initiated actions with money or
@@ -990,6 +995,26 @@ enum TicketDelivery {
 
 // One named person on a group registration, for one main-ticket place. Gets their
 // own quantity-1 ticket and their own attendee form response.
+/// A ticket handed to someone else. oldQrCode is the code that stopped working (null
+/// when one place was split off a shared group ticket, whose code stays valid).
+model TicketTransfer {
+  id             String   @id @default(uuid())
+  ticketId       String
+  fromHolderName String
+  fromUserId     String?
+  toName         String
+  toUserId       String?
+  byUserId       String?
+  oldQrCode      String?
+  createdAt      DateTime @default(now())
+  ticket         Ticket   @relation(fields: [ticketId], references: [id], onDelete: Cascade)
+  toUser         User?    @relation("TransferRecipient", fields: [toUserId], references: [id], onDelete: SetNull)
+  byUser         User?    @relation("TransferActor", fields: [byUserId], references: [id], onDelete: SetNull)
+
+  @@index([ticketId])
+  @@index([oldQrCode])
+}
+
 model Attendee {
   id                   String              @id @default(uuid())
   registrationId       String