fix: nix-deck infinite recursion + add custom-qmd to CI

- Add specialArgs to nix-deck (was missing nixpkgs-unstable, causing
  infinite recursion when roles/local-inference evaluated it)
- Move local-inference import out of roles/default.nix: its module-level
  disabledModules/imports conflict with nix-deck's unstable-based nixpkgs
- Import local-inference directly in zix790prors (the only machine that
  enables it)
- Add custom-qmd and custom-opencode to CI build-and-cache packages

roles/local-inference/default.nix

@@ -14,6 +14,9 @@ let
   llama-server = getExe' llama-cpp-cuda "llama-server";
 in
 {
+  # Replace the stable nixpkgs llama-swap module with the unstable version,
+  # which may have newer features. For systems already built on unstable
+  # (e.g., nix-deck), this module is excluded from roles/default.nix instead.
   imports = [ "${nixpkgs-unstable}/nixos/modules/services/networking/llama-swap.nix" ];
   disabledModules = [ "services/networking/llama-swap.nix" ];