feat: discount toggle flag, hide price from success popup

- Admin: "Добавить скидку" toggle — OFF hides discount fields and sets to 0
- Public: discount line hidden when discountPrice=0
- Success popup: removed price/booking count info

src/components/sections/OpenDay.tsx

@@ -67,10 +67,12 @@ export function OpenDay({ data }: OpenDayProps) {
             <p className="text-lg font-semibold text-white">
               {event.pricePerClass} BYN <span className="text-neutral-400 font-normal text-sm">за занятие</span>
             </p>
-            <p className="text-sm text-gold">
-              <Sparkles size={12} className="inline mr-1" />
-              От {event.discountThreshold} занятий — {event.discountPrice} BYN за каждое!
-            </p>
+            {event.discountPrice > 0 && event.discountThreshold > 0 && (
+              <p className="text-sm text-gold">
+                <Sparkles size={12} className="inline mr-1" />
+                От {event.discountThreshold} занятий — {event.discountPrice} BYN за каждое!
+              </p>
+            )}
           </div>
         </Reveal>