9WAY 2.0.0

PR 6-1: Workshop(Expert) 모델 구현

전문가 과정 모델 계층 구현. TDD 기반. ## 스키마 (티켓 명세 기준) ### expert_courses - level:integer(0-3,12), batch_number:integer - start_date:date, end_date:date - max_participants:integer, status: enum (draft/open/in_progress/completed) - location:string, price:integer, time:string - title:string, slug:string(unique), description:text ### expert_course_applications - applicant_id(FK→users), course_id(FK) - status: enum (pending/approved/rejected/cancelled) - payment_status:string, payment_amount:integer, payment_key:string - unique index: [applicant_id, course_id] ### expert_certificates - user_id(FK), course_id(FK), application_id(FK) - certificate_type: enum (completion/qualification) - certificate_number:string (unique, 형식: 9W-C-YYYY-NQ-NNN) - issued_at:datetime, expires_at:datetime(nullable) ## 주의사항 - Expert 모듈 table_name_prefix "expert_", UUID PK - inverse_of 필수, 슬러그 한국어 fallback - certificate_number 자동 생성 콜백 - fixtures에 _fixture: model_class: