Homework: User registration

As a user, I would like to be able to register as a new user so that I can post my own listings.

NOTES:
- The API to register a new user:
```
POST /api/users/register
BODY
{
"username": "new_username",
"password": "new_password"
}
```

The issue names the registration request POST /api/users/register and its username/password body, but no client files or tests. Locate the registration entry point and API request code, then verify that a new user can submit the form successfully and that the stated request is sent.

Written by the indexing model from the issue text.