- Rewrote the 'sign up for new account with existing username' test in
spec/features/signup_spec.rb.
- Replaced UI-driven setup of an existing user with FactoryBot's `create`.
- Replaced UI navigation with a direct call to `new_member_registration_path`.
- Added an explicit assertion for the 'has already been taken' error
message.
- Ensured a unique email is used for the second signup attempt to isolate
the username validation check.
Co-authored-by: CloCkWeRX <365751+CloCkWeRX@users.noreply.github.com>
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