feat: Linear-style UI redesign with improved mobile experience

Major changes:
- Redesign cabinet with Linear-style components and top navigation
- Replace detail modals with dedicated pages (users, broadcasts, email templates)
- Add email channel support for broadcasts
- Remove pull-to-refresh, improve drag-and-drop on touch devices
- Fix Telegram Mini App: fullscreen, back button, scroll restoration
- Unify admin pages color scheme to design system
- Mobile-first improvements: horizontal tabs for settings, better touch targets

src/components/admin/index.ts

@@ -1,4 +1,6 @@
 // Components
+export * from './AdminBackButton';
+export * from './AdminLayout';
 export * from './icons';
 export * from './Toggle';
 export * from './SettingInput';
@@ -9,6 +11,7 @@ export * from './ThemeTab';
 export * from './FavoritesTab';
 export * from './SettingsTab';
 export * from './SettingsSidebar';
+export * from './SettingsMobileTabs';
 export * from './SettingsSearch';
 
 // Constants and utils