docs: Add no-PR instructions to polecat onboarding (gt-drbd)

Update mol-polecat-work submit-merge step and polecat.md role docs
to explicitly forbid GitHub PRs and direct to beads merge-requests.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

prompts/roles/polecat.md

@@ -91,6 +91,12 @@ bd sync                   # CRITICAL: Push beads changes
 git push origin HEAD      # Push code changes
 ```
 
+**IMPORTANT: No GitHub PRs!**
+- Never use `gh pr create`
+- Never create GitHub pull requests directly
+- The Refinery processes merges via beads merge-request issues
+- After pushing, create: `bd create --type=merge-request --title="Merge: <summary>"`
+
 ### 5. Signal Completion
 After everything is synced and pushed:
 ```