Refactor code structure for improved readability and maintainability

prisma/schema.prisma

@@ -70,6 +70,8 @@ model Novel {
   title         String
   originalTitle String?
   slug          String   @unique
+  seriesId      String?
+  series        Series?  @relation(fields: [seriesId], references: [id], onDelete: SetNull)
   authorName    String   // Tên tác giả nguyên bản của truyện
   originalAuthorName String?
   uploaderId    String?  // Tham chiếu đến User (Mod/Admin) đã upload
@@ -93,6 +95,18 @@ model Novel {
   updatedAt     DateTime @updatedAt
 }
 
+model Series {
+  id          String   @id @default(cuid())
+  name        String
+  slug        String   @unique
+  description String?  @db.Text
+
+  novels      Novel[]
+
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+}
+
 model Genre {
   id          String       @id @default(cuid())
   name        String       @unique