emacs: add pi-coding-agent package

Add dnouri/pi-coding-agent as an Emacs frontend for the pi coding agent.
Pinned to commit 8d8158b.

- Package installed from GitHub with all .el files (includes md-ts-mode)
- Suppress grammar auto-install prompt since tree-sitter grammars are
  already managed by Nix (treesit-grammars.with-all-grammars)
- Keybinding: SPC o p to launch pi-coding-agent
- Alias: M-x pi as shortcut for M-x pi-coding-agent

home/roles/emacs/doom/config.el

@@ -274,6 +274,18 @@ rbw is unavailable or the entry is not found."
                  (error (format "Error listing directory %s: %s" dirpath (error-message-string err)))))
    :args (list '(:name "dirpath" :type "string" :description "Directory path to list"))))
 
+(use-package! pi-coding-agent
+  :commands (pi-coding-agent pi-coding-agent-toggle)
+  :init
+  (defalias 'pi 'pi-coding-agent)
+  (map! :leader
+        (:prefix ("o" . "open")
+         :desc "Pi Coding Agent" "p" #'pi-coding-agent))
+  :config
+  ;; Tree-sitter grammars are managed by Nix (treesit-grammars.with-all-grammars),
+  ;; so suppress the auto-install prompt
+  (setq pi-coding-agent-essential-grammar-action 'warn))
+
 (use-package! claude-code-ide
   :commands (claude-code-ide-menu claude-code-ide-open-here)
   :init