feat: add competition heats system backend

- Add 3 new database tables: divisions, competition_types, event_user_heats
- Add seed data for 6 divisions (NEW, NOV, INT, ADV, ALL, CHA) and 2 competition types (J&J, STR)
- Add API endpoints for divisions and competition types
- Add heats management endpoints in events route (POST/GET/DELETE)
- Implement unique constraint: cannot have same role in same division+competition type
- Add participant verification before allowing heats management
- Support heat numbers 1-9 with optional Leader/Follower role

backend/prisma/schema.prisma

@@ -54,6 +54,7 @@ model User {
   ratingsGiven            Rating[]  @relation("RaterRatings")
   ratingsReceived         Rating[] @relation("RatedRatings")
   eventParticipants       EventParticipant[]
+  heats                   EventUserHeat[]
 
   @@map("users")
 }
@@ -76,6 +77,7 @@ model Event {
   matches           Match[]
   participants      EventParticipant[]
   checkinToken      EventCheckinToken?
+  userHeats         EventUserHeat[]
 
   @@map("events")
 }
@@ -187,3 +189,53 @@ model EventParticipant {
   @@index([eventId])
   @@map("event_participants")
 }
+
+// Competition divisions (Newcomer, Novice, Intermediate, etc.)
+model Division {
+  id           Int             @id @default(autoincrement())
+  name         String          @unique @db.VarChar(50)
+  abbreviation String          @unique @db.VarChar(3)
+  displayOrder Int             @map("display_order")
+
+  // Relations
+  userHeats    EventUserHeat[]
+
+  @@map("divisions")
+}
+
+// Competition types (Jack & Jill, Strictly, etc.)
+model CompetitionType {
+  id           Int             @id @default(autoincrement())
+  name         String          @unique @db.VarChar(50)
+  abbreviation String          @unique @db.VarChar(3)
+
+  // Relations
+  userHeats    EventUserHeat[]
+
+  @@map("competition_types")
+}
+
+// User's declared heats for matchmaking
+model EventUserHeat {
+  id                Int             @id @default(autoincrement())
+  userId            Int             @map("user_id")
+  eventId           Int             @map("event_id")
+  divisionId        Int             @map("division_id")
+  competitionTypeId Int             @map("competition_type_id")
+  heatNumber        Int             @map("heat_number") // 1-9
+  role              String?         @db.VarChar(10) // 'Leader', 'Follower', or NULL
+  createdAt         DateTime        @default(now()) @map("created_at")
+  updatedAt         DateTime        @updatedAt @map("updated_at")
+
+  // Relations
+  user              User            @relation(fields: [userId], references: [id], onDelete: Cascade)
+  event             Event           @relation(fields: [eventId], references: [id], onDelete: Cascade)
+  division          Division        @relation(fields: [divisionId], references: [id])
+  competitionType   CompetitionType @relation(fields: [competitionTypeId], references: [id])
+
+  // Constraint: Cannot have same role in same division+competition type
+  @@unique([userId, eventId, divisionId, competitionTypeId, role])
+  @@index([userId, eventId])
+  @@index([eventId])
+  @@map("event_user_heats")
+}