Highlight Own Duplicate Org Names when Creating an Org

If someone tries to create an org, and there is an existing org name they can access that's very similar to what they already have, highlight (and possibly prevent) that from happening.

Start at the organization-creation flow and trace how existing organizations the user can access are loaded and validated. Determine the expected behavior for similar names, including whether creation should be prevented; done means the agreed behavior is visible and covered by the relevant flow checks.

Written by the indexing model from the issue text.