feat(hotel): many hotels per edition + HotelStay (room assignment)

- Hotel.programId no longer unique (many hotels per edition)
- New HotelStay 1:1 with AttendingMember (hotelId, room, check-in/out)
- Program.hotel -> hotels[]

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

prisma/schema.prisma

@@ -506,7 +506,7 @@ model Program {
   // Grand-finale logistics
   finalistSlotQuotas FinalistSlotQuota[]
   waitlistEntries    WaitlistEntry[]
-  hotel              Hotel?
+  hotels             Hotel[]
   lunchEvent         LunchEvent?
 
   @@unique([name, year])
@@ -2786,6 +2786,7 @@ model AttendingMember {
   flightDetail    FlightDetail?
   visaApplication VisaApplication?
   lunchPick       MemberLunchPick?
+  hotelStay       HotelStay?
 
   @@unique([confirmationId, userId])
   @@index([userId])
@@ -2802,7 +2803,7 @@ enum FlightDetailStatus {
 
 model Hotel {
   id        String   @id @default(cuid())
-  programId String   @unique // 1:1 — one hotel per edition
+  programId String // many hotels per edition
   name      String
   address   String?  @db.Text
   link      String? // external URL to hotel page / booking confirmation
@@ -2810,7 +2811,28 @@ model Hotel {
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
 
-  program Program @relation(fields: [programId], references: [id], onDelete: Cascade)
+  program Program     @relation(fields: [programId], references: [id], onDelete: Cascade)
+  stays   HotelStay[]
+
+  @@index([programId])
+}
+
+/// Per-attendee hotel/room assignment (1:1 with AttendingMember, mirrors FlightDetail).
+model HotelStay {
+  id                String    @id @default(cuid())
+  attendingMemberId String    @unique
+  hotelId           String
+  roomNumber        String?
+  checkInAt         DateTime?
+  checkOutAt        DateTime?
+  notes             String?   @db.Text
+  createdAt         DateTime  @default(now())
+  updatedAt         DateTime  @updatedAt
+
+  attendingMember AttendingMember @relation(fields: [attendingMemberId], references: [id], onDelete: Cascade)
+  hotel           Hotel           @relation(fields: [hotelId], references: [id], onDelete: Restrict)
+
+  @@index([hotelId])
 }
 
 model FlightDetail {