feat(education): complete Flyway migration and atomic submit

sql/postgresql/education/009-education-idempotency-unified-rollback.sql

@@ -0,0 +1,13 @@
+-- =============================================
+-- Education 模块 — 统一幂等表 回滚
+-- Migration: 009 回滚
+-- =============================================
+
+DROP TABLE IF EXISTS education_idempotency;
+
+-- Recreate the original split tables from 003 + 004 migrations if needed:
+-- (restore from backup or re-run 003 and 004 DDL scripts)
+
+-- Remove review_fingerprint column
+ALTER TABLE education_practice_session
+    DROP COLUMN IF EXISTS review_fingerprint;