STYLE: Use consistent 'AI-agent-assisted' terminology throughout admonition

Replace 'agent-created PR' with 'AI-agent-assisted PR' to match the
opening sentence of the admonition block.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: hjmjohnson

Documentation/docs/contributing/index.md

@@ -244,7 +244,7 @@ effectively.
 
 ```{important}
 **Please open AI-agent-assisted pull requests in Draft mode.** We prefer that
-an agent-created PR not be converted to *Ready for Review* until the human
+an AI-agent-assisted PR not be converted to *Ready for Review* until the human
 author has personally verified that:
 
 - all automated CI tests pass,