feat: add booking management, Open Day, unified signup modal

- MC registrations: notification toggles (confirm/remind) with urgency
- Group bookings: save to DB from BookingModal, admin CRUD at /admin/bookings
- Open Day: full event system with schedule grid (halls × time), per-class
  booking, discount pricing (30 BYN / 20 BYN from 3+), auto-cancel threshold
- Unified SignupModal replaces 3 separate forms — consistent fields
  (name, phone, instagram, telegram), Instagram DM fallback on network error
- Centralized /admin/bookings page with 3 tabs (classes, MC, Open Day),
  collapsible sections, notification toggles, filter chips
- Unread booking badge on sidebar + dashboard widget with per-type breakdown
- Pricing: contact hint (Instagram/Telegram/phone) on price & rental tabs,
  admin toggle to show/hide
- DB migrations 5-7: group_bookings table, open_day tables, unified fields

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/app/admin/_components/NotifyToggle.tsx

@@ -0,0 +1,71 @@
+"use client";
+
+import { Bell, CheckCircle2 } from "lucide-react";
+import type { LucideIcon } from "lucide-react";
+
+function Toggle({
+  done,
+  urgent,
+  icon: Icon,
+  label,
+  onToggle,
+}: {
+  done: boolean;
+  urgent: boolean;
+  icon: LucideIcon;
+  label: string;
+  onToggle: () => void;
+}) {
+  return (
+    <button
+      type="button"
+      onClick={onToggle}
+      title={label}
+      className={`relative flex items-center gap-1 rounded-full px-2 py-0.5 text-[10px] font-medium transition-all ${
+        done
+          ? "bg-emerald-500/15 text-emerald-400 border border-emerald-500/30"
+          : urgent
+            ? "bg-red-500/15 text-red-400 border border-red-500/30 pulse-urgent"
+            : "bg-neutral-700/50 text-neutral-400 border border-white/10 hover:border-white/25 hover:text-white"
+      }`}
+    >
+      <Icon size={10} />
+      {label}
+    </button>
+  );
+}
+
+export function NotifyToggle({
+  confirmed,
+  reminded,
+  confirmUrgent,
+  reminderUrgent,
+  onToggleConfirm,
+  onToggleReminder,
+}: {
+  confirmed: boolean;
+  reminded: boolean;
+  confirmUrgent?: boolean;
+  reminderUrgent?: boolean;
+  onToggleConfirm: () => void;
+  onToggleReminder: () => void;
+}) {
+  return (
+    <div className="flex items-center gap-1.5">
+      <Toggle
+        done={confirmed}
+        urgent={confirmUrgent ?? !confirmed}
+        icon={CheckCircle2}
+        label="Подтверждение"
+        onToggle={onToggleConfirm}
+      />
+      <Toggle
+        done={reminded}
+        urgent={reminderUrgent ?? false}
+        icon={Bell}
+        label="Напоминание"
+        onToggle={onToggleReminder}
+      />
+    </div>
+  );
+}