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/styles/animations.css

@@ -324,6 +324,21 @@
   z-index: 1;
 }
 
+/* ===== Notification Pulse ===== */
+
+@keyframes pulse-urgent {
+  0%, 100% {
+    box-shadow: 0 0 0 0 rgba(239, 68, 68, 0.5);
+  }
+  50% {
+    box-shadow: 0 0 0 6px rgba(239, 68, 68, 0);
+  }
+}
+
+.pulse-urgent {
+  animation: pulse-urgent 1.5s ease-in-out infinite;
+}
+
 /* ===== Section Divider ===== */
 
 .section-divider {