Report more specific permissions errors

When initializing a project, if the CLI runs into permissions errors trying to write to directories not owned by the current user, we return just a "Permission error (os 13)" (on macOS). More details here would help end users find the offending directories and rectify permissions issues more easily.

Start by reproducing project initialization on macOS with a directory the current user cannot write to, then trace where the CLI turns the operating-system error into the generic permission message. The work is done when the error identifies the offending directory or directories and the existing initialization behavior remains intact.

Written by the indexing model from the issue text.