discoverLocation root bypasses workspace discovery

Chose returning { path: "." } immediately for an exact root input over validating workspaceNames first, because root publishing has no possible workspace classification and must work when Craft workspace discovery is unavailable. Trap: routing root through getWorkspaceNames() looks uniformly fail-closed, but a broken or unavailable craft workspace list blocks valid root releases unnecessarily. Fix: only exact "." bypasses discovery; every non-root path must still discover and validate workspace names, then fail closed on discovery errors. Input path validation remains upstream in detailsFromContext() before workflow location resolution.