Add codex 0.92.0 PR patch and fix deprecation warnings

- Add nixpkgs PR 483705 to bump codex from 0.89.0 to 0.92.0
- Disable overlay version overrides in favor of PR patches
- Replace deprecated pkgs.system with pkgs.stdenv.hostPlatform.system
- Replace deprecated xfce.thunar with thunar

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

nixos/code.nix

@@ -78,7 +78,7 @@ makeEnable config "myModules.code" true {
     nixd
     nil
     alejandra
-  ] ++ (if pkgs.system == "x86_64-linux" then with pkgs; [
+  ] ++ (if pkgs.stdenv.hostPlatform.system == "x86_64-linux" then with pkgs; [
     # purescript
     purescript
     # Broken