feat(actualbudget): add NixOS guest

modules/services/actualbudget.nix

@@ -0,0 +1,61 @@
+{
+  config,
+  lib,
+  ...
+}:
+let
+  cfg = config.modules.services.actualbudget;
+in
+{
+  options.modules.services.actualbudget = {
+    enable = lib.mkEnableOption "Actual Budget";
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 5006;
+      description = "Port Actual Budget listens on.";
+    };
+
+    dataDir = lib.mkOption {
+      type = lib.types.str;
+      default = "/data";
+      description = "Directory where Actual Budget stores server and user files.";
+    };
+
+    user = lib.mkOption {
+      type = lib.types.str;
+      default = "actual";
+      description = "User account that runs Actual Budget.";
+    };
+
+    uid = lib.mkOption {
+      type = lib.types.ints.positive;
+      default = 20001;
+      description = "Fixed uid for the Actual Budget service user.";
+    };
+
+    group = lib.mkOption {
+      type = lib.types.str;
+      default = "storage";
+      description = "Group account that owns Actual Budget's writable state.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    users.users.${cfg.user} = {
+      isSystemUser = true;
+      uid = cfg.uid;
+      group = cfg.group;
+    };
+
+    services.actual = {
+      enable = true;
+      openFirewall = true;
+      user = cfg.user;
+      group = cfg.group;
+      settings = {
+        inherit (cfg) port dataDir;
+      };
+    };
+  };
+}