- Add DefaultBranch field to RoleData struct
- Update refinery.md.tmpl to use {{ .DefaultBranch }} template variable
- Populate DefaultBranch from rig config in prime.go and rig/manager.go
- Default to 'main' if not configured
- Add test verifying DefaultBranch rendering in refinery template
Fixes issue where refinery agents merged to master instead of the
configured default branch (e.g., 'develop' or 'develop-cstar').