Guide HTTPS vs SSH When Importing with Requires Auth

If someone tries to import, and picks requires auth, but they also put in an HTTPS URL, we won't use their key since we aren't using SSH to connect. We should guide them more on the right formation of their URL there.

Start by locating the import flow and the form handling the “requires auth” option, then reproduce the case with an HTTPS URL. Done means the interface clearly explains the mismatch between HTTPS and SSH authentication and guides the user toward the correct URL format.

Written by the indexing model from the issue text.