fix(ai-tools): use 'rtk' from 'nixpkgs'

modules/ai-tools/default.nix

@@ -1,15 +1,17 @@
 { lib, config, ... }:
 
 let
-  cfg = config."ai-tools";
   inherit (config.host) username;
   inherit (config.secrets) owner;
 in
 {
   options."ai-tools".enable = lib.mkEnableOption "AI tools";
 
-  config = lib.mkIf cfg.enable {
-    nixpkgs.allowedUnfree = [ "claude-code" ];
+  config = lib.mkIf config."ai-tools".enable {
+    nixpkgs.allowedUnfree = [
+      "claude-code"
+      "rtk"
+    ];
     secrets.opencode = [ "api-key" ];
 
     sops.templates."opencode/auth.json" = {