Add a Workflow nudge to re-read AGENTS.md before opening a PR

The existing self-staleness reminders live inside two extension-pattern
recipes and the release checklist, so a behavior change that fits
neither pattern reaches PR time with no check on this file — exactly
how the parse-flow lines describing the old mutate-the-config behavior
survived the PR #222 review round. The nudge states why grep is the
wrong tool for it: AGENTS.md paraphrases behavior in its own words, so
stale text rarely matches the diff's phrasing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: derek73

AGENTS.md

@@ -7,6 +7,8 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 For non-trivial changes, use a feature branch and open a PR.
 Branch naming: `fix/issue-NNN-short-description` or `feat/short-description`.
 
+Before opening the PR, if the change alters parser behavior or internals, *read* the Architecture, Extension Patterns, and Gotchas sections of this file against the change — don't grep for it: AGENTS.md paraphrases behavior in its own words, so text made stale by a code change rarely matches the code's phrasing (a doc-staleness sweep driven by grep terms from the diff will miss it every time). The same applies when scoping a doc-review pass or a subagent prompt: include AGENTS.md in the list of docs to check, or it won't be checked.
+
 ## Commands
 
 ```bash