refactor(modules/nixos): move stuff around

This makes the module a bit clearer and easier to extend.

modules/nixos/styling.nix

@@ -0,0 +1,43 @@
+{ lib, pkgs, ... }@args:
+let
+  cfg = args.config.jconfig.styling;
+  enable = args.config.jconfig.enable && cfg.enable;
+in
+{
+  config = lib.mkIf enable {
+    boot.plymouth = { inherit (cfg) enable; };
+
+    stylix = {
+      inherit (cfg) enable;
+      image = cfg.wallpaper;
+      base16Scheme = "${pkgs.base16-schemes}/share/themes/gruvbox-dark-hard.yaml";
+      polarity = "dark";
+      fonts = {
+        monospace = {
+          name = "JetBrains Mono";
+          package = pkgs.jetbrains-mono;
+        };
+        sansSerif = {
+          name = "Noto Sans";
+          package = pkgs.noto-fonts;
+        };
+        serif = {
+          name = "Noto Serif";
+          package = pkgs.noto-fonts;
+        };
+        emoji = {
+          package = pkgs.noto-fonts-emoji;
+          name = "Noto Color Emoji";
+        };
+        sizes.popups = 12;
+      };
+      targets = {
+        plymouth = {
+          logoAnimated = false;
+          logo = cfg.bootLogo;
+        };
+        nixvim.enable = false;
+      };
+    };
+  };
+}