feat(matching): add auto-matching system for recording partners

Implement algorithm to match dancers with recorders based on:
- Heat collision avoidance (division + competitionType + heatNumber)
- Buffer time (1 heat after dancing before can record)
- Location preference (same city > same country > anyone)
- Max 3 recordings per person
- Opt-out support (falls to bottom of queue)

New API endpoints:
- PUT /events/:slug/registration-deadline
- PUT /events/:slug/recorder-opt-out
- POST /events/:slug/run-matching
- GET /events/:slug/match-suggestions
- PUT /events/:slug/match-suggestions/:id/status

Database changes:
- Event: registrationDeadline, matchingRunAt
- EventParticipant: recorderOptOut
- RecordingSuggestion: new model for match suggestions

backend/prisma/schema.prisma

@@ -59,29 +59,35 @@ model User {
   ratingsReceived         Rating[] @relation("RatedRatings")
   eventParticipants       EventParticipant[]
   heats                   EventUserHeat[]
+  recordingAssignments    RecordingSuggestion[] @relation("RecorderAssignments")
 
   @@map("users")
 }
 
 // Events table (dance events from worldsdc.com)
 model Event {
-  id                Int       @id @default(autoincrement())
-  slug              String    @unique @default(cuid()) @db.VarChar(50)
-  name              String    @db.VarChar(255)
-  location          String    @db.VarChar(255)
-  startDate         DateTime  @map("start_date") @db.Date
-  endDate           DateTime  @map("end_date") @db.Date
-  worldsdcId        String?   @unique @map("worldsdc_id") @db.VarChar(100)
-  participantsCount Int       @default(0) @map("participants_count")
-  description       String?   @db.Text
-  createdAt         DateTime  @default(now()) @map("created_at")
+  id                   Int       @id @default(autoincrement())
+  slug                 String    @unique @default(cuid()) @db.VarChar(50)
+  name                 String    @db.VarChar(255)
+  location             String    @db.VarChar(255)
+  startDate            DateTime  @map("start_date") @db.Date
+  endDate              DateTime  @map("end_date") @db.Date
+  worldsdcId           String?   @unique @map("worldsdc_id") @db.VarChar(100)
+  participantsCount    Int       @default(0) @map("participants_count")
+  description          String?   @db.Text
+  createdAt            DateTime  @default(now()) @map("created_at")
+
+  // Auto-matching configuration
+  registrationDeadline DateTime? @map("registration_deadline") // When registration closes
+  matchingRunAt        DateTime? @map("matching_run_at")        // When auto-matching was last run
 
   // Relations
-  chatRooms         ChatRoom[]
-  matches           Match[]
-  participants      EventParticipant[]
-  checkinToken      EventCheckinToken?
-  userHeats         EventUserHeat[]
+  chatRooms            ChatRoom[]
+  matches              Match[]
+  participants         EventParticipant[]
+  checkinToken         EventCheckinToken?
+  userHeats            EventUserHeat[]
+  recordingSuggestions RecordingSuggestion[]
 
   @@map("events")
 }
@@ -186,6 +192,7 @@ model EventParticipant {
   userId           Int      @map("user_id")
   eventId          Int      @map("event_id")
   competitorNumber Int?     @map("competitor_number") // Bib number - one per user per event
+  recorderOptOut   Boolean  @default(false) @map("recorder_opt_out") // Opt-out from being a recorder
   joinedAt         DateTime @default(now()) @map("joined_at")
 
   // Relations
@@ -236,10 +243,11 @@ model EventUserHeat {
   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])
+  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])
+  recordingSuggestion RecordingSuggestion?
 
   // Constraint: Cannot have same role in same division+competition type
   @@unique([userId, eventId, divisionId, competitionTypeId, role])
@@ -247,3 +255,23 @@ model EventUserHeat {
   @@index([eventId])
   @@map("event_user_heats")
 }
+
+// Recording suggestions from auto-matching algorithm
+model RecordingSuggestion {
+  id         Int      @id @default(autoincrement())
+  eventId    Int      @map("event_id")
+  heatId     Int      @unique @map("heat_id") // One suggestion per heat
+  recorderId Int?     @map("recorder_id")     // NULL if no match found
+  status     String   @default("pending") @db.VarChar(20) // 'pending', 'accepted', 'rejected', 'not_found'
+  createdAt  DateTime @default(now()) @map("created_at")
+  updatedAt  DateTime @updatedAt @map("updated_at")
+
+  // Relations
+  event    Event          @relation(fields: [eventId], references: [id], onDelete: Cascade)
+  heat     EventUserHeat  @relation(fields: [heatId], references: [id], onDelete: Cascade)
+  recorder User?          @relation("RecorderAssignments", fields: [recorderId], references: [id])
+
+  @@index([eventId])
+  @@index([recorderId])
+  @@map("recording_suggestions")
+}