fix: Lazily fetch external modules only if needed

sw/default.nix

@@ -37,9 +37,6 @@ in
   ];
 
   options.athenix.sw = {
-    # Software submodule for the Athenix system suite. sw.enable enables
-    # base packages and common configuration. Each sw.<type>.enable enables
-    # additional packages and services for that system type.
     enable = mkOption {
       type = lib.types.bool;
       default = false;
@@ -57,8 +54,6 @@ in
     };
 
     type = mkOption {
-      # DEPRECATED: Backwards compatibility for external modules
-      # Use athenix.sw.<type>.enable instead
       type = lib.types.nullOr (lib.types.either lib.types.str (lib.types.listOf lib.types.str));
       default = null;
       description = "DEPRECATED: Use athenix.sw.<type>.enable instead. Legacy type selection.";
@@ -66,7 +61,6 @@ in
     };
 
     extraPackages = mkOption {
-      # Additional packages to install beyond the defaults
       type = lib.types.listOf lib.types.package;
       default = [ ];
       description = ''
@@ -77,7 +71,6 @@ in
     };
 
     excludePackages = mkOption {
-      # Packages to exclude from the default package list
       type = lib.types.listOf lib.types.package;
       default = [ ];
       description = ''