refactor(overlays): get NUR packages from the nur-ryan4yin overlay

myNurPkgs evaluated a second nixpkgs just for four packages. Apply the
NUR repo's own overlay instead, so they come from the host's pkgs.

Darwin's pkgs now gets nixpkgsConfig too: it set nixpkgs.pkgs, which
ignores nixpkgs.config, so only myNurPkgs carried the npm mirror there.

Assisted-by: Claude Code (claude-opus-5-5)

outputs/default.nix

@@ -73,16 +73,6 @@ let
           cudaCapabilities = [ "8.9" ];
         };
       };
-      # NUR packages for this system; modules use `myNurPkgs.dsh` instead of
-      # repeating `nur-ryan4yin.packages.${pkgs.stdenv.hostPlatform.system}`.
-      # Instantiate them with the same Nixpkgs policy as the host so npm
-      # fetchers inside NUR packages also use the mirror.
-      myNurPkgs = import "${inputs.nur-ryan4yin}" {
-        pkgs = import inputs.nixpkgs {
-          inherit system;
-          config = nixpkgsConfig;
-        };
-      };
     };
 
   # This is the args for all the haumea modules in this folder.