refactor: move pi's AGENTS.md concat into the agent-skills module

All four tools' context wiring lives there now; this file just installs
the package.

home/common/programs/pi.nix

@@ -1,32 +1,12 @@
-{
-  config,
-  lib,
-  pkgs,
-  inputs,
-  ...
-}:
+{ pkgs, ... }:
 let
   pi = pkgs.callPackage ../../../pkgs/pi/package.nix { };
-
-  skills = inputs.agent-skills;
-
-  # pi has no `@file` imports in context files, so fragments get concatenated
-  # into one AGENTS.md. Skills need no wiring: pi reads ~/.agents/skills, which
-  # the agent-skills module already links.
-  agentsMd = pkgs.writeText "pi-AGENTS.md" (
-    lib.concatMapStringsSep "\n" builtins.readFile [
-      "${skills}/claude-md/machines/${config.programs.agentSkills.machine}.md"
-      "${skills}/claude-md/operating.md"
-      "${skills}/claude-md/writing.md"
-      "${skills}/claude-md/code-comments.md"
-      "${skills}/claude-md/RTK.md"
-    ]
-  );
 in
 {
-  home.packages = [ pi ];
-
+  # ~/.pi/agent/AGENTS.md comes from the agent-skills home-manager module
+  # (pi has no @file imports, so the module concatenates the shared fragments).
+  # Pi reads skills straight from ~/.agents/skills, which the module links.
   # Settings stay unmanaged: pi writes ~/.pi/agent/settings.json itself from
   # /settings, /trust and `pi config`.
-  home.file.".pi/agent/AGENTS.md".source = agentsMd;
+  home.packages = [ pi ];
 }