nixos/orca: init very simple module

nixos/modules/module-list.nix

···
   ./security/systemd-confinement.nix
   ./security/tpm2.nix
   ./security/wrappers/default.nix
+  ./services/accessibility/orca.nix
   ./services/accessibility/speechd.nix
   ./services/admin/docuum.nix
   ./services/admin/meshcentral.nix

nixos/modules/services/accessibility/orca.nix

···
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.orca;
+  inherit (lib)
+    mkEnableOption
+    mkIf
+    mkPackageOption
+    ;
+in
+{
+  options.services.orca = {
+    enable = mkEnableOption "Orca screen reader";
+    package = mkPackageOption pkgs "orca" { };
+  };
+
+  config = mkIf cfg.enable {
+    environment.systemPackages = [ cfg.package ];
+    services.speechd.enable = true;
+  };
+}