Refactor to resolve react-refresh/only-export-components warnings:
- Move buttonVariants export to separate file (Button.variants.ts)
- Extract WebSocketContext to dedicated context file
- Move useWebSocketContext hook to separate file
- Update imports across affected files
All component files now export only components, improving fast refresh reliability
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
