1. Move inline DB init script to external file (scripts/ci/init_test_database.py)
for better maintainability per djpetti's suggestion.
2. Fail fast in CI when pre-created user login fails instead of falling back
to slow registration. This makes debugging easier - if the CI user doesn't
work, something is wrong with workflow setup and should be fixed there.
Per djpetti's suggestion about developer experience.
The external script is now shared between critical-ui-tests.yml and
extended-ui-tests.yml, reducing duplication.
Co-authored-by: Daniel Petti <djpetti@gmail.com>
