feat: backend database changes for advanced SEO fields

backend/prisma/schema.prisma

@@ -77,6 +77,10 @@ model Product {
   dosageLogic       String?  @map("dosage_logic") @db.Text
   suitableFor       String   @map("suitable_for") @db.VarChar(15) // سگ, گربه, هر دو
   imageUrl          String   @map("image_url") @db.Text
+  metaTitle         String?  @map("meta_title") @db.VarChar(200)
+  metaDescription   String?  @map("meta_description") @db.Text
+  canonicalUrl      String?  @map("canonical_url") @db.Text
+  keywords          String?  @db.Text
   createdAt         DateTime @default(now()) @map("created_at") @db.Timestamptz()
 
   ingredients       ProductIngredient[]