add pi coding agent module

Manages `~/.pi/agent` config via the itme-brain/pi submodule and
provides nodejs_20 with NPM_CONFIG_PREFIX=~/.npm-global so pi and its
extensions install via the global npm ecosystem.

Pi itself and extensions like pi-mcp-adapter are installed manually
via `npm install -g` rather than packaged through nix — the ecosystem
moves too fast to keep derivations current.

.gitmodules

@@ -14,3 +14,6 @@
 	path = user/modules/bash/bash
 	url = https://github.com/itme-brain/bash.git
 	branch = master
+[submodule "user/modules/pi/agent"]
+	path = user/modules/pi/agent
+	url = git@github.com:itme-brain/pi.git

system/machines/desktop/modules/home-manager/home.nix

@@ -81,6 +81,8 @@
         writing.enable = true;
       };
 
+      pi.enable = true;
+
       gui = {
         wm.hyprland.enable = true;
         browser.firefox.enable = true;

user/modules/pi/agent

@@ -0,0 +1 @@
+Subproject commit 71b78ea0c3b64e9fb253a408ad607b4f2d44f86b

user/modules/pi/default.nix

@@ -0,0 +1,28 @@
+{ pkgs, lib, config, ... }:
+
+with lib;
+let
+  cfg = config.modules.user.pi;
+  npmGlobal = "${config.home.homeDirectory}/.npm-global";
+in
+{ options.modules.user.pi = { enable = mkEnableOption "user.pi"; };
+  config = mkIf cfg.enable {
+    home.packages = with pkgs; [ nodejs_20 ];
+
+    home.sessionVariables = {
+      LLAMACPP_BASE_URL = "https://ai.ramos.codes/v1";
+      NPM_CONFIG_PREFIX = npmGlobal;
+    };
+
+    home.sessionPath = [ "${npmGlobal}/bin" ];
+
+    home.file.".pi/agent" = {
+      source = ./agent;
+      recursive = true;
+    };
+
+    programs.bash.initExtra = ''
+      export LLAMACPP_API_KEY=$(cat /run/secrets/LLAMA_API_KEY)
+    '';
+  };
+}