feat: min/max participants — shared ParticipantLimits component

- New ParticipantLimits component in FormField.tsx (reusable)
- Used in both Open Day settings and MC editor — identical layout
- Open Day: event-level min/max (DB migration 15)
- MC: per-event min/max (JSON fields)
- Public: waiting list when full, spots counter, amber success modal

src/components/sections/OpenDay.tsx

@@ -93,6 +93,7 @@ export function OpenDay({ data }: OpenDayProps) {
                   <ClassCard
                     key={cls.id}
                     cls={cls}
+                    maxParticipants={event.maxParticipants}
                     onSignup={setSignup}
                   />
                 ))}
@@ -137,9 +138,11 @@ export function OpenDay({ data }: OpenDayProps) {
 
 function ClassCard({
   cls,
+  maxParticipants = 0,
   onSignup,
 }: {
   cls: OpenDayClass;
+  maxParticipants?: number;
   onSignup: (info: { classId: number; label: string }) => void;
 }) {
   const label = `${cls.style} · ${cls.trainer} · ${cls.startTime}–${cls.endTime}`;
@@ -161,8 +164,10 @@ function ClassCard({
     );
   }
 
+  const isFull = maxParticipants > 0 && cls.bookingCount >= maxParticipants;
+
   return (
-    <div className="rounded-xl border border-white/10 bg-neutral-900 p-4 transition-all hover:border-gold/20">
+    <div className={`rounded-xl border p-4 transition-all ${isFull ? "border-white/5 bg-neutral-900/50" : "border-white/10 bg-neutral-900 hover:border-gold/20"}`}>
       <div className="flex items-start justify-between gap-3">
         <div className="flex-1 min-w-0">
           <span className="text-xs text-gold font-medium">{cls.startTime}–{cls.endTime}</span>
@@ -171,12 +176,21 @@ function ClassCard({
             <Users size={10} />
             {cls.trainer}
           </p>
+          {maxParticipants > 0 && (
+            <p className={`text-[10px] mt-1 ${isFull ? "text-amber-400" : "text-neutral-500"}`}>
+              {cls.bookingCount}/{maxParticipants} мест
+            </p>
+          )}
         </div>
         <button
           onClick={() => onSignup({ classId: cls.id, label })}
-          className="shrink-0 rounded-full bg-gold/10 border border-gold/20 px-4 py-2 text-xs font-medium text-gold hover:bg-gold/20 transition-colors cursor-pointer"
+          className={`shrink-0 rounded-full px-4 py-2 text-xs font-medium transition-colors cursor-pointer ${
+            isFull
+              ? "bg-amber-500/10 border border-amber-500/20 text-amber-400 hover:bg-amber-500/20"
+              : "bg-gold/10 border border-gold/20 text-gold hover:bg-gold/20"
+          }`}
         >
-          Записаться
+          {isFull ? "Лист ожидания" : "Записаться"}
         </button>
       </div>
     </div>