feat: clean up agent config

modules/capabilities/ai/_sources.nix

@@ -1,10 +1,4 @@
 { pkgs }:
 {
-  ponytail = pkgs.fetchFromGitHub {
-    owner = "DietrichGebert";
-    repo = "ponytail";
-    rev = "356918eba965ee1eac64bd3a7f0dd02108350de5";
-    hash = "sha256-LPNMyHsri3+eeDmphEAKL1JgoRE4dLIPfZ4XZ+xu5UY=";
-  };
   herdr = pkgs.llm-agents.herdr.src;
 }