chore: expand a2ui catalog extractor guide

packages/genui/a2ui-catalog-extractor/AGENTS.md

@@ -0,0 +1,14 @@
+# a2ui-catalog-extractor
+
+When editing this package's user documentation, update both `README.md`
+and `readme.zh_cn.md`. The English README is the primary document and the
+Chinese README should remain an equivalent translation, not a shorter
+summary.
+
+Keep README examples tied to tests. If a documented component contract,
+generated schema, CLI flow, or API example changes, update or add a test
+fixture or test case in this package so the documented behavior is checked.
+
+The user-facing READMEs are for external package users only. Do not include
+monorepo setup, workspace commands, current private-package status, or
+repository-maintainer workflow in either README.