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/ent/usersubscription.go

@@ -23,6 +23,8 @@ type UserSubscription struct {
 	CreatedAt time.Time `json:"created_at,omitempty"`
 	// UpdatedAt holds the value of the "updated_at" field.
 	UpdatedAt time.Time `json:"updated_at,omitempty"`
+	// DeletedAt holds the value of the "deleted_at" field.
+	DeletedAt *time.Time `json:"deleted_at,omitempty"`
 	// UserID holds the value of the "user_id" field.
 	UserID int64 `json:"user_id,omitempty"`
 	// GroupID holds the value of the "group_id" field.
@@ -65,9 +67,11 @@ type UserSubscriptionEdges struct {
 	Group *Group `json:"group,omitempty"`
 	// AssignedByUser holds the value of the assigned_by_user edge.
 	AssignedByUser *User `json:"assigned_by_user,omitempty"`
+	// UsageLogs holds the value of the usage_logs edge.
+	UsageLogs []*UsageLog `json:"usage_logs,omitempty"`
 	// loadedTypes holds the information for reporting if a
 	// type was loaded (or requested) in eager-loading or not.
-	loadedTypes [3]bool
+	loadedTypes [4]bool
 }
 
 // UserOrErr returns the User value or an error if the edge
@@ -103,6 +107,15 @@ func (e UserSubscriptionEdges) AssignedByUserOrErr() (*User, error) {
 	return nil, &NotLoadedError{edge: "assigned_by_user"}
 }
 
+// UsageLogsOrErr returns the UsageLogs value or an error if the edge
+// was not loaded in eager-loading.
+func (e UserSubscriptionEdges) UsageLogsOrErr() ([]*UsageLog, error) {
+	if e.loadedTypes[3] {
+		return e.UsageLogs, nil
+	}
+	return nil, &NotLoadedError{edge: "usage_logs"}
+}
+
 // scanValues returns the types for scanning values from sql.Rows.
 func (*UserSubscription) scanValues(columns []string) ([]any, error) {
 	values := make([]any, len(columns))
@@ -114,7 +127,7 @@ func (*UserSubscription) scanValues(columns []string) ([]any, error) {
 			values[i] = new(sql.NullInt64)
 		case usersubscription.FieldStatus, usersubscription.FieldNotes:
 			values[i] = new(sql.NullString)
-		case usersubscription.FieldCreatedAt, usersubscription.FieldUpdatedAt, usersubscription.FieldStartsAt, usersubscription.FieldExpiresAt, usersubscription.FieldDailyWindowStart, usersubscription.FieldWeeklyWindowStart, usersubscription.FieldMonthlyWindowStart, usersubscription.FieldAssignedAt:
+		case usersubscription.FieldCreatedAt, usersubscription.FieldUpdatedAt, usersubscription.FieldDeletedAt, usersubscription.FieldStartsAt, usersubscription.FieldExpiresAt, usersubscription.FieldDailyWindowStart, usersubscription.FieldWeeklyWindowStart, usersubscription.FieldMonthlyWindowStart, usersubscription.FieldAssignedAt:
 			values[i] = new(sql.NullTime)
 		default:
 			values[i] = new(sql.UnknownType)
@@ -149,6 +162,13 @@ func (_m *UserSubscription) assignValues(columns []string, values []any) error {
 			} else if value.Valid {
 				_m.UpdatedAt = value.Time
 			}
+		case usersubscription.FieldDeletedAt:
+			if value, ok := values[i].(*sql.NullTime); !ok {
+				return fmt.Errorf("unexpected type %T for field deleted_at", values[i])
+			} else if value.Valid {
+				_m.DeletedAt = new(time.Time)
+				*_m.DeletedAt = value.Time
+			}
 		case usersubscription.FieldUserID:
 			if value, ok := values[i].(*sql.NullInt64); !ok {
 				return fmt.Errorf("unexpected type %T for field user_id", values[i])
@@ -266,6 +286,11 @@ func (_m *UserSubscription) QueryAssignedByUser() *UserQuery {
 	return NewUserSubscriptionClient(_m.config).QueryAssignedByUser(_m)
 }
 
+// QueryUsageLogs queries the "usage_logs" edge of the UserSubscription entity.
+func (_m *UserSubscription) QueryUsageLogs() *UsageLogQuery {
+	return NewUserSubscriptionClient(_m.config).QueryUsageLogs(_m)
+}
+
 // Update returns a builder for updating this UserSubscription.
 // Note that you need to call UserSubscription.Unwrap() before calling this method if this UserSubscription
 // was returned from a transaction, and the transaction was committed or rolled back.
@@ -295,6 +320,11 @@ func (_m *UserSubscription) String() string {
 	builder.WriteString("updated_at=")
 	builder.WriteString(_m.UpdatedAt.Format(time.ANSIC))
 	builder.WriteString(", ")
+	if v := _m.DeletedAt; v != nil {
+		builder.WriteString("deleted_at=")
+		builder.WriteString(v.Format(time.ANSIC))
+	}
+	builder.WriteString(", ")
 	builder.WriteString("user_id=")
 	builder.WriteString(fmt.Sprintf("%v", _m.UserID))
 	builder.WriteString(", ")