Improve the behavior when joining a group

[nickyito]

Description

Criteria

• Error handling

  • Show a pop-up with an error message if a user has already joined.
  • Show a pop-up with an error message if the invitation code is expired.

• If the user is a non-logged-in or non-registered user, the user is redirected to the login page. After logging in, they are automatically redirected to the joining group page.

Notes