fix(monthly-comparison): 0일 0h 수정 + 관리자 검토 태깅

- getAllStatus: daily_attendance_records JOIN으로 실제 근무일/시간 집계
- vacation_days: vacation_types.deduct_days SUM (반차 0.5 정확 반영)
- admin_checked 컬럼 + POST /admin-check API (upsert 패턴)
- 상태 뱃지 라벨: 미검토/확인요청/수정요청/반려/확인완료

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

system1-factory/api/db/migrations/20260401_monthly_confirm_workflow.sql

@@ -4,3 +4,4 @@ ALTER TABLE monthly_work_confirmations
 ALTER TABLE monthly_work_confirmations ADD COLUMN IF NOT EXISTS reviewed_by INT NULL;
 ALTER TABLE monthly_work_confirmations ADD COLUMN IF NOT EXISTS reviewed_at TIMESTAMP NULL;
 ALTER TABLE monthly_work_confirmations ADD COLUMN IF NOT EXISTS change_details TEXT NULL;
+ALTER TABLE monthly_work_confirmations ADD COLUMN IF NOT EXISTS admin_checked TINYINT(1) DEFAULT 0;