kayla: seed chrome's GTK theme via initial_preferences next to the binary

hosts/FredOS-Kayla.nix

@@ -3,6 +3,27 @@
 # FredOS-Gaming/FredOS-Macbook and stay off here). Windows refugees get a
 # taskbar, a start menu and a settings app that look like what they left.
 { config, pkgs, lib, ... }:
+let
+  # Under KDE, Chrome's GetDefaultSystemTheme() (ui/linux/linux_ui_factory.cc)
+  # hardcodes SystemTheme::kQt for every KDE* desktop — it reads only the
+  # detected desktop environment. No policy and no command-line switch changes
+  # that default (--ui-toolkit picks which backend gets built, not the pref),
+  # so the profile pref is the only lever.
+  #
+  # Chrome seeds a new profile from `initial_preferences`, which it looks for
+  # in DIR_EXE — the directory holding the binary (first_run_internal_linux.cc)
+  # — so it has to be baked into the package, not dropped in /etc. Everything
+  # outside the "distribution" key is copied into the profile on first run.
+  #
+  # system_theme: 0 = Classic, 1 = GTK, 2 = Qt (ui/color/system_theme.h).
+  chromeGtkDefault = pkgs.google-chrome.overrideAttrs (old: {
+    postInstall = (old.postInstall or "") + ''
+      cp ${pkgs.writeText "chrome-initial-preferences" (builtins.toJSON {
+        extensions.theme.system_theme = 1;
+      })} $out/share/google/chrome/initial_preferences
+    '';
+  });
+in
 {
   config = lib.mkIf (config.networking.hostName == "FredOS-Kayla") {
     services.displayManager.sddm = {
@@ -59,12 +80,7 @@
     stylix.targets.chromium.enable = false;
 
     environment.systemPackages = with pkgs; [
-      # Chrome picks its toolkit from the desktop environment, and under KDE
-      # that's the Qt backend (hence the libqt{5,6}_shim.so it ships) — which
-      # is what's drawing the odd decorations. --ui-toolkit overrides that
-      # detection, so it uses GTK, i.e. the adw-gtk3 theme stylix already
-      # writes. No manual trip through Settings → Appearance.
-      (google-chrome.override { commandLineArgs = "--ui-toolkit=gtk"; })
+      chromeGtkDefault
       spotify
       vesktop
       faugus-launcher