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/default.nix

@@ -1,4 +1,8 @@
-{ lib, pkgs, ... }:
+{
+  lib,
+  pkgs,
+  ...
+}:
 
 with lib;
 
@@ -11,7 +15,9 @@ with lib;
     ./desktop
     ./k3s-node
     ./kodi
-    ./local-inference
+    # local-inference is NOT imported here because its module-level
+    # disabledModules/imports conflict with nix-deck's unstable-based
+    # nixpkgs. Import it directly in machine configs that need it.
     ./nfs-mounts
     ./plasma-bigscreen
     ./nvidia