feat: implement API client and user authentication storage

[devdeen213]

What's done:

• Removed default Expo boilerplate (components, screens, hooks)
• Simplified project structure for scalability
• Set up centralized axios instance with base URL from env (EXPO_PUBLIC_API_URL)
• Added request/response interceptors (including token injection)
• Implemented a reusable useApi hook for managing API state (loading, error, data)
• Defined a scalable API module pattern (services/ directory)
• Added example usage in HomeScreen
• Integrated Expo Secure Store for token storage

closes #85

[zakkiyyat]

Looks good thanks for the effort.