refactor: moved nixos modules to dendrite pattern

modules/nixos/programs/actual/actual.nix

@@ -0,0 +1,25 @@
+{...}: {
+  flake.nixosModules.actual-service = {
+    lib,
+    config,
+    ...
+  }: let
+    dataDirectory = "/var/lib/private/actual";
+  in {
+    options.services.actual = {
+      port = lib.mkOption {
+        type = lib.types.port;
+        description = "The port to listen on";
+        default = 5006;
+      };
+    };
+    config = lib.mkIf config.services.actual.enable {
+      services.actual = {
+        settings = {
+          port = config.services.actual.port;
+          dataDir = dataDirectory;
+        };
+      };
+    };
+  };
+}