fix(数据层): 修复数据完整性与仓储一致性问题

## 数据完整性修复 (fix-critical-data-integrity)
- 添加 error_translate.go 统一错误转换层
- 修复 nil 输入和 NotFound 错误处理
- 增强仓储层错误一致性

## 仓储一致性修复 (fix-high-repository-consistency)
- Group schema 添加 default_validity_days 字段
- Account schema 添加 proxy edge 关联
- 新增 UsageLog ent schema 定义
- 修复 UpdateBalance/UpdateConcurrency 受影响行数校验

## 数据卫生修复 (fix-medium-data-hygiene)
- UserSubscription 添加软删除支持 (SoftDeleteMixin)
- RedeemCode/Setting 添加硬删除策略文档
- account_groups/user_allowed_groups 的 created_at 声明 timestamptz
- 停止写入 legacy users.allowed_groups 列
- 新增迁移: 011-014 (索引优化、软删除、孤立数据审计、列清理)

## 测试补充
- 添加 UserSubscription 软删除测试
- 添加迁移回归测试
- 添加 NotFound 错误测试

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/internal/repository/group_repo.go

@@ -42,7 +42,8 @@ func (r *groupRepository) Create(ctx context.Context, groupIn *service.Group) er
 		SetSubscriptionType(groupIn.SubscriptionType).
 		SetNillableDailyLimitUsd(groupIn.DailyLimitUSD).
 		SetNillableWeeklyLimitUsd(groupIn.WeeklyLimitUSD).
-		SetNillableMonthlyLimitUsd(groupIn.MonthlyLimitUSD)
+		SetNillableMonthlyLimitUsd(groupIn.MonthlyLimitUSD).
+		SetDefaultValidityDays(groupIn.DefaultValidityDays)
 
 	created, err := builder.Save(ctx)
 	if err == nil {
@@ -79,6 +80,7 @@ func (r *groupRepository) Update(ctx context.Context, groupIn *service.Group) er
 		SetNillableDailyLimitUsd(groupIn.DailyLimitUSD).
 		SetNillableWeeklyLimitUsd(groupIn.WeeklyLimitUSD).
 		SetNillableMonthlyLimitUsd(groupIn.MonthlyLimitUSD).
+		SetDefaultValidityDays(groupIn.DefaultValidityDays).
 		Save(ctx)
 	if err != nil {
 		return translatePersistenceError(err, service.ErrGroupNotFound, service.ErrGroupExists)
@@ -89,7 +91,7 @@ func (r *groupRepository) Update(ctx context.Context, groupIn *service.Group) er
 
 func (r *groupRepository) Delete(ctx context.Context, id int64) error {
 	_, err := r.client.Group.Delete().Where(group.IDEQ(id)).Exec(ctx)
-	return err
+	return translatePersistenceError(err, service.ErrGroupNotFound, nil)
 }
 
 func (r *groupRepository) List(ctx context.Context, params pagination.PaginationParams) ([]service.Group, *pagination.PaginationResult, error) {
@@ -239,8 +241,8 @@ func (r *groupRepository) DeleteCascade(ctx context.Context, id int64) ([]int64,
 	// err 为 dbent.ErrTxStarted 时，复用当前 client 参与同一事务。
 
 	// Lock the group row to avoid concurrent writes while we cascade.
-	// 这里使用 exec.QueryContext 手动扫描，确保同一事务内加锁并能区分“未找到”与其他错误。
-	rows, err := exec.QueryContext(ctx, "SELECT id FROM groups WHERE id = $1 FOR UPDATE", id)
+	// 这里使用 exec.QueryContext 手动扫描，确保同一事务内加锁并能区分"未找到"与其他错误。
+	rows, err := exec.QueryContext(ctx, "SELECT id FROM groups WHERE id = $1 AND deleted_at IS NULL FOR UPDATE", id)
 	if err != nil {
 		return nil, err
 	}
@@ -263,7 +265,8 @@ func (r *groupRepository) DeleteCascade(ctx context.Context, id int64) ([]int64,
 
 	var affectedUserIDs []int64
 	if groupSvc.IsSubscriptionType() {
-		rows, err := exec.QueryContext(ctx, "SELECT user_id FROM user_subscriptions WHERE group_id = $1", id)
+		// 只查询未软删除的订阅，避免通知已取消订阅的用户
+		rows, err := exec.QueryContext(ctx, "SELECT user_id FROM user_subscriptions WHERE group_id = $1 AND deleted_at IS NULL", id)
 		if err != nil {
 			return nil, err
 		}
@@ -282,7 +285,8 @@ func (r *groupRepository) DeleteCascade(ctx context.Context, id int64) ([]int64,
 			return nil, err
 		}
 
-		if _, err := exec.ExecContext(ctx, "DELETE FROM user_subscriptions WHERE group_id = $1", id); err != nil {
+		// 软删除订阅：设置 deleted_at 而非硬删除
+		if _, err := exec.ExecContext(ctx, "UPDATE user_subscriptions SET deleted_at = NOW() WHERE group_id = $1 AND deleted_at IS NULL", id); err != nil {
 			return nil, err
 		}
 	}
@@ -297,18 +301,11 @@ func (r *groupRepository) DeleteCascade(ctx context.Context, id int64) ([]int64,
 		return nil, err
 	}
 
-	// 3. Remove the group id from users.allowed_groups array (legacy representation).
-	// Phase 1 compatibility: also delete from user_allowed_groups join table when present.
+	// 3. Remove the group id from user_allowed_groups join table.
+	// Legacy users.allowed_groups 列已弃用，不再同步。
 	if _, err := exec.ExecContext(ctx, "DELETE FROM user_allowed_groups WHERE group_id = $1", id); err != nil {
 		return nil, err
 	}
-	if _, err := exec.ExecContext(
-		ctx,
-		"UPDATE users SET allowed_groups = array_remove(allowed_groups, $1) WHERE $1 = ANY(allowed_groups)",
-		id,
-	); err != nil {
-		return nil, err
-	}
 
 	// 4. Delete account_groups join rows.
 	if _, err := exec.ExecContext(ctx, "DELETE FROM account_groups WHERE group_id = $1", id); err != nil {