fix: Code for category

internal/domain/category.go

@@ -1,6 +1,7 @@
 package domain
 
 import (
+	"regexp"
 	"time"
 
 	"github.com/google/uuid"
@@ -11,8 +12,19 @@ import (
 type Category struct {
 	ID          uuid.UUID  `json:"id"`
 	ParentID    *uuid.UUID `json:"parent_id"`
+	Code        string     `json:"code"`
 	Name        string     `json:"name"`
 	Description string     `json:"description"`
 	CreatedAt   time.Time  `json:"created_at"`
 	UpdatedAt   time.Time  `json:"updated_at"`
 }
+
+// slugPattern matches a slug: lowercase latin letters and digits in
+// dash-separated groups, e.g. "population", "land-use-2024".
+var slugPattern = regexp.MustCompile(`^[a-z0-9]+(?:-[a-z0-9]+)*$`)
+
+// ValidSlug reports whether s is a valid slug (lowercase latin letters, digits,
+// and single dashes between groups; no leading, trailing, or repeated dashes).
+func ValidSlug(s string) bool {
+	return slugPattern.MatchString(s)
+}