Implement responsive UI components and contextual title management:

- Add `BottomNav`, `MobileHeader`, `DesktopHeader`, and `Sidebar` for improved layout and navigation.
- Introduce `TitleContext` to manage page titles dynamically across components.
- Extract `PrivateRoute` to a reusable component for authenticated route handling.
- Enhance PWA support with the `usePwa` hook, improving standalone detection and adaptive UI behavior.
- Refactor `App.tsx` for modularity and streamlined layout handling.