feat(special-curation): complete implementation with all components

- Database: SpecialSong model with startTime
- Backend: API endpoints for curation
- Admin: Waveform editor and curation page
- Game: startTime support in AudioPlayer
- UI: Curate button in admin dashboard

prisma/schema.prisma

@@ -19,7 +19,7 @@ model Song {
   createdAt DateTime @default(now())
   puzzles   DailyPuzzle[]
   genres    Genre[]
-  specials  Special[]
+  specials  SpecialSong[]
 }
 
 model Genre {
@@ -35,10 +35,22 @@ model Special {
   maxAttempts Int      @default(7)
   unlockSteps String   // JSON array: "[2,4,7,11,16,30,60]"
   createdAt   DateTime @default(now())
-  songs       Song[]
+  songs       SpecialSong[]
   dailyPuzzles DailyPuzzle[]
 }
 
+model SpecialSong {
+  id        Int     @id @default(autoincrement())
+  specialId Int
+  special   Special @relation(fields: [specialId], references: [id], onDelete: Cascade)
+  songId    Int
+  song      Song    @relation(fields: [songId], references: [id], onDelete: Cascade)
+  startTime Int     @default(0) // Start time in seconds
+  order     Int?    // For manual ordering
+
+  @@unique([specialId, songId])
+}
+
 model DailyPuzzle {
   id        Int      @id @default(autoincrement())
   date      String   // Format: YYYY-MM-DD