Add rules to the agent to have it run code checking.

It needs to fix code style problems in addition to type
errors. Hopefully, this should smooth out some of the pain points.

AGENTS.md

@@ -57,6 +57,10 @@ This repository is a screen reader. Prioritize accessibility, correctness, and s
 - If you edit a `#!/usr/bin/env bash`, `#!/bin/bash`, or POSIX `sh` script, run `shellcheck` and fix issues.
 - Avoid colorized output unless explicitly requested (accessibility-first; keep scripts simple).
 
+## Python Rules
+- When making changes to the codebase, you **must** run `ruff check` and fix all problems therein.
+- Additionally, you **must** run `ty check` and **must** fix all errors therein.
+
 ## Plugins (Cthulhu)
 - System plugins live in `src/cthulhu/plugins/`.
 - Follow existing plugin patterns (keybinding registration, GTK dialog/window patterns, debug logging).