Implement authentication token management and session handling

Commit notes

- Refactored login and registration mutations to store access and refresh tokens upon successful authentication. - Added a logout mutation to clear tokens and cached queries, enhancing user session management. - Introduced a session expiration handler that listens for auth events, notifying users when their session has expired. - Updated token management to export constants for access and refresh token keys, improving code maintainability.

This commit enhances the authentication flow and user experience by ensuring proper token handling and session management.