feat: implement new layout components and routing structure

- Added HeaderLayout component for the application header.
- Introduced KeepAliveViewport for managing tab states and rendering.
- Created TabNav for tab navigation with animated indicator.
- Removed old Tabs component in favor of new layout structure.
- Updated routing with AppRouter and defined appTabs for navigation.
- Enhanced theme context to manage dark mode styles.
- Added new UI components: Badge, Button, Separator, and Tabs.
- Refactored pages to utilize new layout components and improve responsiveness.
- Updated global styles for better theming and layout consistency.
- Introduced TypeScript path aliases for cleaner imports.

frontend/src/contexts/index.ts

@@ -1,5 +1,2 @@
 export { ThemeProvider } from './ThemeContext';
 export { useTheme } from './useTheme';
-export { AppProvider } from './AppContext';
-export type { AppContextValue, TabId } from './app-context';
-export { useApp } from './useApp';