[FRONTEND] Fix email regex for verification

[choden-dev]

Is your feature request related to a problem? Please describe.

Right now users can forget the .com at the end of the email and still make it to the confirmation stage, not a big deal because the account can't be created but should still be fixed

change the email verification in client/src/store/SignUpForm.tsx

BEFORE MERGING

• Storybooks created where possible
• Tested with nock if data fetching
• Tests written for critical interactions
• PR Reviewed (For non-trivial changes)
• Changes tested after rebasing on master or merging in master (hint: git fetch origin master:master, then git rebase master or git merge master)
• All required PR checks passing