nixos/comfyui: append extraArgs after the module's own arguments

The module writes its own flags into services.comfyui.extraArgs, the
option users write to as well. List definitions are concatenated and the
module's landed last, so a flag set by the user was overridden by the
module instead of overriding it:

    comfyui '--port=9999' '--base-directory=/srv/comfyui' \
      '--base-directory=/var/lib/comfyui' … '--port=8188'

Both of the user's flags are overwritten as argparse keeps the last occurrence of each.

Assisted-by: Claude Code:claude-opus-5 (mostly)
Co-authored-by: ilyusha <121713022+rokokol@users.noreply.github.com>

nixos/modules/services/misc/comfyui.nix

@@ -52,7 +52,7 @@ in
   };
 
   config = lib.mkIf cfg.enable {
-    services.comfyui.extraArgs = [
+    services.comfyui.extraArgs = lib.mkBefore [
       "--base-directory=/var/lib/comfyui"
       "--database-url=sqlite:////var/lib/comfyui/user/comfyui.db"
       "--listen=${lib.concatStringsSep "," cfg.listen}"