Add Nix flake for mcrctl

Vendor dependencies and expose mcrctl binary via nix build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/github.com/go-chi/chi/v5/middleware/supress_notfound.go

@@ -0,0 +1,27 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/go-chi/chi/v5"
+)
+
+// SupressNotFound will quickly respond with a 404 if the route is not found
+// and will not continue to the next middleware handler.
+//
+// This is handy to put at the top of your middleware stack to avoid unnecessary
+// processing of requests that are not going to match any routes anyway. For
+// example its super annoying to see a bunch of 404's in your logs from bots.
+func SupressNotFound(router *chi.Mux) func(next http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			rctx := chi.RouteContext(r.Context())
+			match := rctx.Routes.Match(rctx, r.Method, r.URL.Path)
+			if !match {
+				router.NotFoundHandler().ServeHTTP(w, r)
+				return
+			}
+			next.ServeHTTP(w, r)
+		})
+	}
+}