⚡ (analytics) Improve analytics graph accuracy

packages/prisma/mysql/schema.prisma

@@ -274,6 +274,7 @@ model Answer {
   createdAt   DateTime @default(now()) @updatedAt
   resultId    String
   blockId     String
+  itemId      String?
   groupId     String
   variableId  String?
   content     String   @db.Text
@@ -281,7 +282,7 @@ model Answer {
   result      Result   @relation(fields: [resultId], references: [id], onDelete: Cascade)
 
   @@unique([resultId, blockId, groupId])
-  @@index([groupId])
+  @@index([blockId, itemId])
   @@index([storageUsed])
 }