First step of the go-chi -> go-pkgz/routegroup migration. The HTTP->HTTPS
redirect and ACME http-01 challenge routers are small, self-contained
http.Handlers separate from the main API router, so they move cleanly:
- chi.NewRouter() -> routegroup.New(http.NewServeMux())
- middleware.Throttle -> rest.Throttle (same concurrency-limit semantics)
- middleware.Timeout -> local timeout helper (context deadline, mirrors chi)
- drop middleware.RealIP: these routers do redirect/challenge only, with no
per-IP logic, so the spoofable header trust is simply removed here
- return http.Handler instead of chi.Router (callers already take http.Handler)
chi stays a dependency (still used by the main API router); this only removes
its use from ssl.go. go test -race, vet, golangci-lint and govulncheck clean.