Enhance life add command

Currently the "life add" command aborts if a life file is not present and the user is starting fresh but wants to add a dotfiles repository. The "onlyRepo" case in lifeAdd function should be enhanced to handle this.

@vrom911 @chshersh Thoughts on this? Would this be an acceptable addition?

Start with the `life add` command and the `onlyRepo` case in `lifeAdd`, reproducing the fresh-start situation where no life file exists. The work is done when adding a dotfiles repository succeeds without an existing life file, while preserving the command's existing behavior in other cases.

Written by the indexing model from the issue text.