Refactor routing and update AuthPage layout for improved user experience

Commit notes

- Removed redundant route definitions for `_layout.tsx` and `index.tsx`, consolidating them for clarity. - Updated `AuthPage` layout to enhance navigation and visual structure, including a new hero image and improved button placements. - Refactored authentication forms to streamline user interactions and improve accessibility. - Adjusted theme colors in `root.tsx` for better visual consistency across the application.