feat: Round 23 - Practice exercises, enhanced virtual character, inter-school federation, voice chat

- Practice exercises: AI-generated multiple choice questions, practice mode with score tracking
- Enhanced virtual character: More animations, accessories, AI chat integration, XP system
- Inter-school federation: School leaderboard, team scores, federation competitions
- Enhanced communication: Voice chat, file sharing, note sharing, teacher notes panel
- Added isFederation and federationSchedule fields to Competition model
- 170+ new i18n keys
- All lints pass

prisma/schema.prisma

@@ -1680,6 +1680,8 @@ model Competition {
   rules          String?  // markdown rules/description
   isPublic       Boolean  @default(false) // visible to all schools?
   isDemo         Boolean  @default(false)
+  isFederation   Boolean  @default(false) // inter-school district federation competition
+  federationSchedule String? // "weekly" | "monthly" | "quarterly"
   createdById    String   // teacher/admin who created
   createdAt      DateTime @default(now())
   updatedAt      DateTime @updatedAt