Runestone Issue: Registration allows emoji-only values for name fields

[harrisonj2-v]

What Page were you on
https://runestone.academy/admin/auth/register

Describe the bug
The account registration form allows users to create an account using only a single emoji for the name fields.

A Screenshot is worth a thousand words

What is your username
harrisonj2-v

[bnmnetp]

Fixed in 149683d, alongside #1305.

Name fields must now contain at least one letter or digit, which rejects an emoji-only name. The check uses Python's str.isalnum, which is Unicode-aware, so this deliberately does not restrict names to ASCII or to Latin script — José, 王, and Ólafsdóttir all still register, and I verified that. Ruling out emoji while ruling in real names from any writing system was the tricky part; a naive "letters only" rule would have locked out a lot of legitimate students.

An emoji alongside a real name (Ada 🎉) is still allowed. Only values with no letter or digit at all are refused.