docs: add status_set tool instruction example

Author: ammar-agent

docs/AGENTS.md

@@ -155,3 +155,7 @@ gh pr view <number> --json mergeable,mergeStateStatus | jq '.'
 
 - When Plan Mode is requested, assume the user wants the actual completed plan; do not merely describe how you would devise one.
 - Attach a net LoC estimate (product code only) to each recommended approach.
+
+## Tool: status_set
+
+- Set status url to the Pull Request once opened