Add auth identity legacy backfill and email sync

backend/internal/repository/user_repo_integration_test.go

@@ -26,6 +26,8 @@ func (s *UserRepoSuite) SetupTest() {
 	s.repo = newUserRepositoryWithSQL(s.client, integrationDB)
 
 	// 清理测试数据，确保每个测试从干净状态开始
+	_, _ = integrationDB.ExecContext(s.ctx, "DELETE FROM auth_identity_channels")
+	_, _ = integrationDB.ExecContext(s.ctx, "DELETE FROM auth_identities")
 	_, _ = integrationDB.ExecContext(s.ctx, "DELETE FROM user_subscriptions")
 	_, _ = integrationDB.ExecContext(s.ctx, "DELETE FROM user_allowed_groups")
 	_, _ = integrationDB.ExecContext(s.ctx, "DELETE FROM users")