extract stylix to separate module, add nixos module with auto-import

nix/hm-module.nix

@@ -7,40 +7,6 @@ self:
 }:
 let
   cfg = config.programs.nova-shell;
-
-  stylixAvailable = config ? lib && config.lib ? stylix;
-
-  stylixTheme =
-    let
-      c = config.lib.stylix.colors.withHashtag;
-      f = config.stylix.fonts;
-    in
-    {
-      colors = {
-        inherit (c)
-          base00
-          base01
-          base02
-          base03
-          base04
-          base05
-          base06
-          base07
-          base08
-          base09
-          base0A
-          base0B
-          base0C
-          base0D
-          base0E
-          base0F
-          ;
-      };
-      fontFamily = f.sansSerif.name;
-      fontSize = f.sizes.desktop;
-      barOpacity = 1.0 - config.stylix.opacity.desktop;
-      iconFontFamily = "Symbols Nerd Font";
-    };
 in
 {
   options.programs.nova-shell = {
@@ -295,7 +261,7 @@ in
         Keys: colors (base00-base0F), fontFamily, iconFontFamily, fontSize,
         barOpacity, barHeight, barPadding, groupSpacing, groupPadding, moduleSpacing,
         radius, screenRadius, reducedMotion.
-        Automatically populated from stylix when it is available.
+        Populated from stylix when homeModules.stylix is imported.
       '';
     };
 
@@ -327,11 +293,8 @@ in
         cfg.modules;
 
     xdg.configFile."nova-shell/theme.json".source =
-      let
-        stylixDefaults = if stylixAvailable then stylixTheme else { };
-        finalTheme = lib.recursiveUpdate stylixDefaults cfg.theme;
-      in
-      (pkgs.formats.json { }).generate "nova-shell-theme.json" finalTheme;
+      (pkgs.formats.json { }).generate "nova-shell-theme.json"
+        cfg.theme;
 
     # Niri layer rules for backdrop placement (requires niri-flake hm module)
     programs.niri.settings.layer-rules = lib.mkIf (config ? programs && config.programs ? niri) [