Get rid of fetchPrimaryOrganization from lib/auth/auth.ts

Right now when we call getUser, if it is not an API token (i.e. the Supabase JWT token), we guess which organization the user cares about.

Instead, we should always make the `orgName` explicit, basically telling you which page we're coming from. This will make sure we don't have side effect issues (e.g. with the auto-cache)