Extract a single shared parseGitHost (packages/ui/src/lib/gitHost.ts) used
by both the custom-domain registry (normalizeProviderDomain) and remote
detection (gitProvider). Previously both parsers required a user@ prefix,
rejecting valid bare scp remotes like codeberg.org:owner/repo.git, and
mangled IPv6 hosts. Now scp forms with or without a user, ssh:// URLs with
ports, git+ssh scheme, and bracketed/unbracketed IPv6 all normalize to a
bare hostname; Windows-path-like input is rejected.