Build mobile expense template

Implement foundation for a fintech mobile app with Tailwind, Vite, React: - Add toolbar header with optional back button - Create bottom navigation (Home, Pay, Profile) - Layout glue components and pages (Home, Pay) scaffolding - Wire up Layout wrapper and basic UI components (Card, Button, NavLink) - Set up design system tokens and color theming in CSS and tailwind config X-Lovable-Edit-ID: edt-19b75b87-4563-4ded-b562-773c3d8458ca