feat: contact page improvements, Yandex map from addresses

- Instagram field: @username input with API validation (like team page)
- Phone validation: blocks auto-save when incomplete, shows warning
- SectionEditor: validate prop to conditionally block saves
- Yandex Map: auto-generated from addresses via Nominatim geocoding,
  dark theme, no API key needed
- Schedule: address hint linking to Contacts
- Renamed "Всплывающие окна" → "Формы записи", moved after Записи

src/app/admin/layout.tsx

@@ -30,6 +30,7 @@ const NAV_ITEMS = [
   { href: "/admin", label: "Дашборд", icon: LayoutDashboard },
   { href: "/admin/meta", label: "SEO / Мета", icon: Globe },
   { href: "/admin/bookings", label: "Записи", icon: ClipboardList },
+  { href: "/admin/popups", label: "Формы записи", icon: MessageSquare },
   // Sections follow user-side order: Hero → About → Classes → Team → OpenDay → Schedule → Pricing → MC → News → FAQ → Contact
   { href: "/admin/hero", label: "Главный экран", icon: Sparkles },
   { href: "/admin/about", label: "О студии", icon: FileText },
@@ -41,7 +42,6 @@ const NAV_ITEMS = [
   { href: "/admin/master-classes", label: "Мастер-классы", icon: Star },
   { href: "/admin/news", label: "Новости", icon: Newspaper },
   { href: "/admin/faq", label: "FAQ", icon: HelpCircle },
-  { href: "/admin/popups", label: "Всплывающие окна", icon: MessageSquare },
   { href: "/admin/contact", label: "Контакты", icon: Phone },
 ];