Drop-in swap of the global concurrency limiter (go-pkgz/rest.Throttle has the same signature and semantics as chi's middleware.Throttle), with the chi router left in place. First of the per-middleware swaps that chip away at go-chi/chi/v5/middleware before the router itself is migrated. chi/middleware is still imported for RealIP/Timeout/NoCache; build, vet, race tests and golangci-lint clean.