fix: allow unfree packages to resolve VS Code build failure

- Add 'nixpkgs.config.allowUnfree = true' to core/system/default.nix for global NixOS configuration.
- Add 'nixpkgs.config.allowUnfree = true' to features/default.nix for Home Manager package set.
- This resolves evaluation errors when VS Code is included in the build.

core/system/default.nix

@@ -19,4 +19,6 @@
   ];
 
   time.timeZone = lib.mkDefault config.nomarchy.system.timezone;
+
+  nixpkgs.config.allowUnfree = true;
 }