Add guildhall

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

services/guildhall.nix

@@ -0,0 +1,16 @@
+# services/guildhall.nix — Guildhall, the co-op idle game for friends.
+#
+# The game and NixOS module live in the standalone guildhall flake. nginx is
+# the only public listener; Authelia admits any account, and the game keys
+# each player on the Remote-User it passes through. Nightly snapshots sit
+# next to flowtrack's on the SSD branch of the pool.
+{ config, lib, ... }:
+{
+  config = lib.mkIf (config.networking.hostName == "FredOS-Mediaserver") {
+    services.guildhall = {
+      enable = true;
+      port = 8098;
+      backup.directory = "/mnt/disk2/backups/guildhall";
+    };
+  };
+}