meta(agents): Update AI commit attribution guidance (#21166)

Clarify that AI commits should use the committer email associated with
the agent instead of assuming Anthropic-only attribution. Document known
OpenAI and Cursor committer emails, and allow omitting the attribution
line only when no committer email is known.

This will prevent stuff like this from happening

<img width="814" height="127" alt="image"
src="https://github.com/user-attachments/assets/286705c1-5810-46c1-8ef2-063605655e01"
/>

Co-authored-by: GPT-5 Codex <codex@openai.com>

Author: szokeasaurusrex

AGENTS.md

@@ -44,12 +44,16 @@ Single package: `cd packages/<name> && yarn test`
 
 ## Commit Attribution
 
-AI commits MUST include:
+AI commits MUST include a `Co-Authored-By` line with the appropriate committer email when known:
 
 ```
-Co-Authored-By: <agent model name> <noreply@anthropic.com>
+Co-Authored-By: <Claude model name> <noreply@anthropic.com>
+Co-Authored-By: <OpenAI/ChatGPT model name> <codex@openai.com>
+Co-Authored-By: <Cursor agent name> <cursoragent@cursor.com>
 ```
 
+Use the Cursor email for Cursor, even when it runs a Claude or OpenAI model. Omit the line only when there is no known committer email address for the agent.
+
 ## Git Workflow
 
 Uses **Git Flow** (see `docs/gitflow.md`).