When contributing to upstream repos or wanting human review before merge,
the --no-merge flag keeps polecat work on a feature branch instead of
auto-merging to main.
Changes:
- Add --no-merge flag to gt sling command
- Store no_merge field in bead's AttachmentFields
- Modify gt done to skip merge queue when no_merge is set
- Push branch and mail dispatcher "READY_FOR_REVIEW" instead
- Add tests for field parsing and sling flag storage
Closes: gt-p7b8
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>