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/primitives/Popover/index.ts

@@ -0,0 +1,10 @@
+export {
+  Popover,
+  PopoverTrigger,
+  PopoverAnchor,
+  PopoverClose,
+  PopoverContent,
+  PopoverArrow,
+  type PopoverContentProps,
+  type PopoverArrowProps,
+} from './Popover';