Add lxc-tor-relay build type with nyx monitoring

New tor-relay build type (currently lxc-only) running a plain Tor
middle relay via modules/tor/enable-relay.nix, plus nyx for
interactive monitoring over the relay's control socket.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

hosts/tor-relay/host.nix

@@ -0,0 +1,12 @@
+_:
+
+{
+  networking.hostName = "tor-relay";
+
+  # No networking.hostId: only ZFS-touching hosts (server, docker) need one
+  # for pool-import safety, and this host does neither.
+
+  # A genuinely new host (not a pre-refactor carry-over), so it tracks the
+  # flake's current nixpkgs release rather than being pinned to an older one.
+  system.stateVersion = "26.05";
+}