Initial addition of the Arcade study feature. Add connections as the first working game.

prisma/schema.prisma

@@ -18,6 +18,7 @@ model Class {
   quizSets             QuizSet[]
   materialGroups       MaterialGroup[]
   spacedRepetitionSets SpacedRepetitionSet[]
+  arcadePacks          ArcadePack[]
 }
 
 model Deck {
@@ -146,12 +147,52 @@ model Setting {
 
 model StudyActivity {
   id         String   @id @default(uuid())
-  type       String // "FLASHCARD" | "QUIZ_QUESTION"
+  type       String // "FLASHCARD" | "QUIZ_QUESTION" | "ARCADE_GROUP"
   occurredAt DateTime @default(now())
 
   @@index([occurredAt])
 }
 
+model ArcadePack {
+  id                   String   @id @default(uuid())
+  classId              String
+  gameType             String
+  name                 String
+  description          String?
+  schemaVersion        Int
+  sourceJson           String
+  normalizedJson       String
+  validationReportJson String
+  sortOrder            Int      @default(0)
+  createdAt            DateTime @default(now())
+  updatedAt            DateTime @updatedAt
+
+  class    Class           @relation(fields: [classId], references: [id], onDelete: Cascade)
+  attempts ArcadeAttempt[]
+
+  @@index([classId, gameType, sortOrder])
+}
+
+model ArcadeAttempt {
+  id              String   @id @default(uuid())
+  arcadePackId    String
+  mode            String
+  score           Int
+  maxScore        Int
+  accuracy        Float
+  durationSeconds Int
+  mistakes        Int
+  hintsUsed       Int
+  settingsJson    String
+  resultsJson     String
+  seed            String
+  completedAt     DateTime @default(now())
+
+  arcadePack ArcadePack @relation(fields: [arcadePackId], references: [id], onDelete: Cascade)
+
+  @@index([arcadePackId, completedAt])
+}
+
 model MaterialGroup {
   id        String   @id @default(uuid())
   classId   String