Tolerate trailing slash in cluster publicUrl

hostFromPublicURL rejected any non-empty path, so a catalog entry like https://aws-us-east-2.entire.io/ (Path == "/") was dropped in clustersToRegions — silently removing clusters and risking "no regions available to mirror into" if the control plane emits trailing slashes. publicUrl is a trusted catalog field, so accept a bare "/" path; real paths/queries/fragments/userinfo are still refused. (Trail review)