- Add OrderRelationType enum (UNASSIGNED, LEGACY, FIRST, CONTINUED, NEUTRAL)
- Create play_clerk_customer_relation table to track first-completed history
- Add order_relation_type column to play_order_info
- Migrate existing orders to set relation types based on completion history
- Update order services to determine relation type on creation
- Update order VOs and controllers to expose relation type in API responses
- Update clerk performance calculations to account for relation types
- Update revenue calculations to distinguish between first and continued orders
- Add comprehensive API and unit tests for order relation functionality
