fix: make category slug optional

backend/prisma/migrations/20260518051754_make_slug_optional/migration.sql

@@ -0,0 +1,2 @@
+-- AlterTable
+ALTER TABLE "HealthCheckCategory" ALTER COLUMN "slug" DROP NOT NULL;

backend/prisma/schema.prisma

@@ -224,7 +224,7 @@ model NewsImage {
 model HealthCheckCategory {
   id          Int             @id @default(autoincrement())
   name        String          @unique 
-  slug        String          @unique
+  slug        String?          @unique
   description String?
   isActive    Boolean         @default(true)
   sortOrder   Int             @default(1000)