explorerUrl() hardcoded both the seed ("iris.radicle.network") and
the explorer base ("https://radicle.network"), so every "Copy Link"
and "Open in …" action ignored the user's config and could point at
a host that does not replicate the repo.
Expose publicExplorer and preferredSeeds on the Config type (both
already carried by radicle::profile::Config) and thread config
through to every explorerUrl() call site. URLs are now built from
the publicExplorer template, filling $host from the first preferred
seed (falling back to rosa only when none are configured), and link
labels show the configured explorer's host.
Co-authored-by: Rūdolfs Ošiņš <rudolfs@osins.org>
