breathe-configreload

The ConfigReloadCluster Cluster impl — breathe's CONFIG-FILE-RELOAD I/O boundary. The hands that carve a `key = value` config line and trigger the matching reload (pgbouncer RELOAD, nginx/PostgreSQL SIGHUP, or a deferred restart) for a LimitLayout::ConfigFile band. Mirrors HostCluster; reuses the one BandProvider. Side effects abstracted behind the ConfigReloadEnv trait (the typed-spec-triplet testability seam).