Add hostname package to nettest nix container

Alpine provides hostname via busybox; nix needs it explicitly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

containers/nettest/default.nix

@@ -14,6 +14,7 @@ let
       pkgs.dnsutils # provides nslookup, dig
       pkgs.cacert
       pkgs.coreutils
+      pkgs.hostname
       pkgs.bashInteractive
     ];
   };