feat: clean up agent config

modules/capabilities/ai.nix

@@ -33,11 +33,6 @@ in
         };
 
         features.plugins = true;
-        marketplaces.nix-managed = {
-          source_type = "local";
-          source = "${ai.marketplace}";
-        };
-        plugins."ponytail@nix-managed".enabled = true;
         hooks = ai.codexHooks;
         mcp_servers = ai.servers // {
           context7 = ai.servers.context7 // {
@@ -196,11 +191,6 @@ in
         ) ai.skills
         // {
           ".codex/AGENTS.md".text = builtins.readFile ./ai/instructions/codex.md;
-          # Codex's installed-plugin scanner skips symlinked version directories.
-          "${ai.codexCache}" = {
-            source = ai.sources.ponytail;
-            recursive = true;
-          };
         };
     };
 }