Consolidate build URL helpers into helpers/url with auth flag

Summary

Refactor and consolidate git auth URL helper logic by moving it from the common package to the helpers/url package. This enables re-use for the scripts-to-steps migration and removes dead code identified in the helpers/url package during the move.

Background

The git auth URL helper currently lives in the common package. To support the scripts-to-steps migration, this logic needs to be accessible from helpers/url. During the refactor, dead code was also identified in the helpers/url package that should be cleaned up.

Tasks

• Move git auth URL helper from common package to helpers/url package
• Add an auth flag to the consolidated URL helper
• Remove dead code from helpers/url package
• Ensure existing tests from common package continue to pass
• Add dedicated tests to the helpers/url package
• Refactor duplicate tests so the same logic isn't tested twice

References

• MR: !6483 (merged)