-- =============================================
-- Education 模块 — 收藏夹 DDL Rollback (PostgreSQL)
-- Migration: 007
-- =============================================
-- IMPORTANT: This is a documentation-only rollback.
--   No DROP/ALTER/DELETE statements are executed. The favorite
--   table is provenance-safe: it only accumulates user preference
--   data. Dropping this table would lose student favorites with
--   no recovery path.
--
-- What this migration created:
--   - education_favorite (new table)
--   - idx_tenant_user (index)
--   - idx_tenant_user_target_type (index)
--   - uk_tenant_user_target (unique constraint)
--
-- Manual rollback requires:
--   1. Verified database backup before rollback
--   2. Operator approval (DBA sign-off)
--   3. Provenance of all favorite records preserved (exported)
--   4. Soft-delete via deleted = true before any hard drop
--
-- These tables are NOT deleted by this script. Favorite history is
-- retained; if deletion is required by external policy, consult
-- the DBA for a verified rollback procedure.