Implement Authentication Flow with React Navigation and AsyncStorage

[cscouto]

This PR implements the full authentication flow for the Experient React Native take-home assignment. Users can log in, persist their session, and access the main app. The solution follows the assignment requirements precisely and removes leftover Expo Router configuration.

Changes Included:

1. Authentication Flow:

• Login screen with Username, Password, and Login button.
• On login, simulates API request to /auth/login using the provided mock payload.
• Parses simulated Set-Cookie headers into accessToken and refreshToken.
• Session persistence using AsyncStorage with token expiry handling.
• Conditional rendering of the app based on authentication state.

2. Navigation:

• Added React Navigation with two stacks:
• AuthStack → Login screen
• AppStack → Home screen
• Auth state controls which stack is displayed.
• State Management:
• Used React Context + useReducer to manage authentication state.
• Handles login, logout, and session restoration on app launch.

3. Storage:

• Persisted accessToken, refreshToken, and tokenExpiry in AsyncStorage.
• Session is restored if tokens exist and are not expired.

4. Project Cleanup:

• Removed Expo Router and all related configurations.
• Deleted app/ folder to prevent route conflicts.
• Updated package.json main entry to "node_modules/expo/AppEntry.js".
• Updated app.json to remove web.output: "static" which was causing Expo Router errors.
• Ensured App.tsx is the root entry point for React Navigation.

5. Screens:

• LoginScreen → Handles login and validation.
• HomeScreen → Placeholder main screen with logout button.