- Add ReviewState enum (pending, approved, changes_requested, etc.)
- Add DEFAULT_REVISION constant for git HEAD references
- service/pr/reviews.rs: use ReviewState for review creation and
submission state validation
- service/pr/core.rs: use MergeStrategyKind for merge strategy
selection
- service/im/stages.rs: use StagePrivacyLevel for stage creation
- service/im/invitations.rs: use Role enum for invitation role
defaults
zhenyi