Add default settings file support for Dank Material Shell (DMS)

- Introduced a new option `defaultSettingsFile` in the DMS configuration to allow host-specific first-run settings.
- Updated the home-manager module to read from the specified settings file if provided, otherwise falling back to the bundled defaults.
- Enhanced the documentation in the default settings file to clarify its purpose and usage.

modules/desktop/shells/dms/default.nix

@@ -38,6 +38,15 @@
         example = [ "sudo" "nixos-rebuild" "switch" "--flake" ".#14900k" ];
         description = "Command used by DMS nix-monitor widget for rebuild actions.";
       };
+      defaultSettingsFile = lib.mkOption {
+        type = lib.types.nullOr lib.types.path;
+        default = null;
+        example = ./dms-default-settings.json;
+        description = ''
+          Host-specific first-run `settings.json` seed. When set, replaces the bundled
+          `default-settings.nix` template on fresh profiles.
+        '';
+      };
     };
   };
 
@@ -85,6 +94,7 @@
         ])
         ++ (cfg.extraRightBarWidgets or [ ]);
       programs.nix-monitor.rebuildCommand = rebuildCommand;
+      dms.defaultSettingsFile = cfg.defaultSettingsFile or null;
     };
   };
 }