- types/index.ts: Task status 'progressing' → 'undergoing' + 'completed'; Milestone status updated to open/freeze/undergoing/completed/closed + started_at field
- MilestoneFormModal: dropdown options updated
- MilestoneDetailPage: isProgressing → isUndergoing, badge class simplified
- MilestonesPage: badge class simplified
- TaskDetailPage: status transition map updated for new state machine