Apply for offer

- Allow user to click on the "Apply" button
- When user apply for an offer, send a request to the backend with the offer id and refresh the current screen or update the displayed data if request success
- Redirect to login screen if a user is not logged in

Locate the offer screen and its Apply control, then trace the existing backend request and login-routing entry points before changing anything. Done means the offer id is submitted, successful application data is reflected on the current screen, and unauthenticated users are redirected to login.

Written by the indexing model from the issue text.