stylix: add accent color

I spent an hour just to add one f*ing option

modules/user/packages/drvs/ags.nix

@@ -1,15 +1,11 @@
-{ stdenv, lib, config, colors, username, ... }:
+{ stdenv, colors, accent ? colors.base0B, ... }:
   stdenv.mkDerivation {
     name = "AGS theme";
 
     src = ./ags;
     dontUnpack = true;
 
-    patchPhase = let
-      accent = if username == "chest"
-        then colors.base0E
-        else colors.base0B;
-    in ''
+    patchPhase = ''
       echo \$bg:       \#${colors.base00}\;  > colors.scss
       echo \$surface0: \#${colors.base02}\; >> colors.scss
       echo \$fg:       \#${colors.base05}\; >> colors.scss

modules/user/stylix.nix

@@ -0,0 +1,40 @@
+{ config, lib, ... }: let
+  inherit (lib) mkOption types;
+
+  base16Names = [
+    "base00"
+    "base01"
+    "base02"
+    "base03"
+    "base04"
+    "base05"
+    "base06"
+    "base07"
+    "base08"
+    "base09"
+    "base0A"
+    "base0B"
+    "base0C"
+    "base0D"
+    "base0E"
+    "base0F"
+  ];
+in {
+  options.stylix.accent = mkOption {
+    type = types.enum base16Names;
+    default = "base0B";
+    description = ''
+      Base16 colour used as the user accent.
+
+      Use it as:
+
+        config.lib.stylix.colors.${config.stylix.accent}
+        config.lib.stylix.colors.withHashtag.${config.stylix.accent}
+
+      This module deliberately does not extend config.lib.stylix.colors: Stylix
+      exports that value as a generated base16 attrset/functor, and replacing or
+      partially extending it can break Stylix targets which expect metadata such
+      as `scheme` to be present.
+    '';
+  };
+}