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/app/admin/open-day/page.tsx

@@ -5,6 +5,7 @@ import {
   Plus, X, Loader2, Calendar, Trash2, Ban, CheckCircle2, RotateCcw,
 } from "lucide-react";
 import { adminFetch } from "@/lib/csrf";
+import { ParticipantLimits } from "../_components/FormField";
 
 // --- Types ---
 
@@ -17,6 +18,7 @@ interface OpenDayEvent {
   discountPrice: number;
   discountThreshold: number;
   minBookings: number;
+  maxParticipants: number;
   active: boolean;
 }
 
@@ -128,18 +130,12 @@ function EventSettings({
         </div>
       </div>
 
-      <div className="grid gap-4 sm:grid-cols-2">
-        <div>
-          <label className="block text-sm text-neutral-400 mb-1.5">Мин. записей на занятие</label>
-          <input
-            type="number"
-            value={event.minBookings}
-            onChange={(e) => onChange({ minBookings: parseInt(e.target.value) || 1 })}
-            className="w-full rounded-lg border border-white/10 bg-neutral-800 px-4 py-2.5 text-white outline-none focus:border-gold transition-colors"
-          />
-          <p className="text-[10px] text-neutral-600 mt-1">Если записей меньше — занятие можно отменить</p>
-        </div>
-      </div>
+      <ParticipantLimits
+        min={event.minBookings}
+        max={event.maxParticipants ?? 0}
+        onMinChange={(v) => onChange({ minBookings: v })}
+        onMaxChange={(v) => onChange({ maxParticipants: v })}
+      />
 
       <div className="flex items-center gap-3 pt-1">
         <button
@@ -185,13 +181,12 @@ function ClassCell({
   const [trainer, setTrainer] = useState(cls.trainer);
   const [style, setStyle] = useState(cls.style);
   const [endTime, setEndTime] = useState(cls.endTime);
-  const [maxPart, setMaxPart] = useState(cls.maxParticipants);
 
   const atRisk = cls.bookingCount < minBookings && !cls.cancelled;
 
   function save() {
     if (trainer.trim() && style.trim()) {
-      onUpdate(cls.id, { trainer: trainer.trim(), style: style.trim(), endTime, maxParticipants: maxPart });
+      onUpdate(cls.id, { trainer: trainer.trim(), style: style.trim(), endTime });
       setEditing(false);
     }
   }
@@ -209,15 +204,9 @@ function ClassCell({
           <option value="">Тренер...</option>
           {trainers.map((t) => <option key={t} value={t}>{t}</option>)}
         </select>
-        <div className="flex gap-2">
-          <div className="flex-1">
-            <label className="text-[10px] text-neutral-500 mb-0.5 block">До</label>
-            <input type="time" value={endTime} onChange={(e) => setEndTime(e.target.value)} className={selectCls} />
-          </div>
-          <div className="flex-1">
-            <label className="text-[10px] text-neutral-500 mb-0.5 block">Макс. чел.</label>
-            <input type="number" min={0} value={maxPart} onChange={(e) => setMaxPart(parseInt(e.target.value) || 0)} placeholder="0 = без лимита" className={selectCls} />
-          </div>
+        <div>
+          <label className="text-[10px] text-neutral-500 mb-0.5 block">До</label>
+          <input type="time" value={endTime} onChange={(e) => setEndTime(e.target.value)} className={selectCls} />
         </div>
         <div className="flex gap-1 justify-end">
           <button onClick={() => setEditing(false)} className="text-[10px] text-neutral-500 hover:text-white px-1">
@@ -255,7 +244,7 @@ function ClassCell({
               ? "text-red-400"
               : "text-emerald-400"
         }`}>
-          {cls.bookingCount}{cls.maxParticipants > 0 ? `/${cls.maxParticipants}` : ""} чел.
+          {cls.bookingCount} чел.
         </span>
         {atRisk && !cls.cancelled && (
           <span className="text-[9px] text-red-400">мин. {minBookings}</span>
@@ -500,6 +489,7 @@ export default function OpenDayAdminPage() {
       discountPrice: 20,
       discountThreshold: 3,
       minBookings: 4,
+      maxParticipants: 0,
       active: true,
     });
   }