feat(server): allow multiple session attach to doc (#12933)

fix AI-236

packages/backend/server/schema.prisma

@@ -443,6 +443,7 @@ model AiSession {
   messageCost     Int       @default(0)
   tokenCost       Int       @default(0)
   createdAt       DateTime  @default(now()) @map("created_at") @db.Timestamptz(3)
+  updatedAt       DateTime  @default(now()) @updatedAt @map("updated_at") @db.Timestamptz(3)
   deletedAt       DateTime? @map("deleted_at") @db.Timestamptz(3)
 
   user     User               @relation(fields: [userId], references: [id], onDelete: Cascade)