refactor: use dtos in controllers

backend/internal/model/base.go

@@ -8,8 +8,8 @@ import (
 
 // Base contains common columns for all tables.
 type Base struct {
-	ID        string    `gorm:"primaryKey;not null" json:"id"`
-	CreatedAt time.Time `json:"createdAt"`
+	ID        string `gorm:"primaryKey;not null"`
+	CreatedAt time.Time
 }
 
 func (b *Base) BeforeCreate(_ *gorm.DB) (err error) {