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/user/user.go

@@ -49,6 +49,8 @@ const (
 	EdgeAssignedSubscriptions = "assigned_subscriptions"
 	// EdgeAllowedGroups holds the string denoting the allowed_groups edge name in mutations.
 	EdgeAllowedGroups = "allowed_groups"
+	// EdgeUsageLogs holds the string denoting the usage_logs edge name in mutations.
+	EdgeUsageLogs = "usage_logs"
 	// EdgeUserAllowedGroups holds the string denoting the user_allowed_groups edge name in mutations.
 	EdgeUserAllowedGroups = "user_allowed_groups"
 	// Table holds the table name of the user in the database.
@@ -86,6 +88,13 @@ const (
 	// AllowedGroupsInverseTable is the table name for the Group entity.
 	// It exists in this package in order to avoid circular dependency with the "group" package.
 	AllowedGroupsInverseTable = "groups"
+	// UsageLogsTable is the table that holds the usage_logs relation/edge.
+	UsageLogsTable = "usage_logs"
+	// UsageLogsInverseTable is the table name for the UsageLog entity.
+	// It exists in this package in order to avoid circular dependency with the "usagelog" package.
+	UsageLogsInverseTable = "usage_logs"
+	// UsageLogsColumn is the table column denoting the usage_logs relation/edge.
+	UsageLogsColumn = "user_id"
 	// UserAllowedGroupsTable is the table that holds the user_allowed_groups relation/edge.
 	UserAllowedGroupsTable = "user_allowed_groups"
 	// UserAllowedGroupsInverseTable is the table name for the UserAllowedGroup entity.
@@ -308,6 +317,20 @@ func ByAllowedGroups(term sql.OrderTerm, terms ...sql.OrderTerm) OrderOption {
 	}
 }
 
+// ByUsageLogsCount orders the results by usage_logs count.
+func ByUsageLogsCount(opts ...sql.OrderTermOption) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborsCount(s, newUsageLogsStep(), opts...)
+	}
+}
+
+// ByUsageLogs orders the results by usage_logs terms.
+func ByUsageLogs(term sql.OrderTerm, terms ...sql.OrderTerm) OrderOption {
+	return func(s *sql.Selector) {
+		sqlgraph.OrderByNeighborTerms(s, newUsageLogsStep(), append([]sql.OrderTerm{term}, terms...)...)
+	}
+}
+
 // ByUserAllowedGroupsCount orders the results by user_allowed_groups count.
 func ByUserAllowedGroupsCount(opts ...sql.OrderTermOption) OrderOption {
 	return func(s *sql.Selector) {
@@ -356,6 +379,13 @@ func newAllowedGroupsStep() *sqlgraph.Step {
 		sqlgraph.Edge(sqlgraph.M2M, false, AllowedGroupsTable, AllowedGroupsPrimaryKey...),
 	)
 }
+func newUsageLogsStep() *sqlgraph.Step {
+	return sqlgraph.NewStep(
+		sqlgraph.From(Table, FieldID),
+		sqlgraph.To(UsageLogsInverseTable, FieldID),
+		sqlgraph.Edge(sqlgraph.O2M, false, UsageLogsTable, UsageLogsColumn),
+	)
+}
 func newUserAllowedGroupsStep() *sqlgraph.Step {
 	return sqlgraph.NewStep(
 		sqlgraph.From(Table, FieldID),

backend/ent/user/where.go

@@ -895,6 +895,29 @@ func HasAllowedGroupsWith(preds ...predicate.Group) predicate.User {
 	})
 }
 
+// HasUsageLogs applies the HasEdge predicate on the "usage_logs" edge.
+func HasUsageLogs() predicate.User {
+	return predicate.User(func(s *sql.Selector) {
+		step := sqlgraph.NewStep(
+			sqlgraph.From(Table, FieldID),
+			sqlgraph.Edge(sqlgraph.O2M, false, UsageLogsTable, UsageLogsColumn),
+		)
+		sqlgraph.HasNeighbors(s, step)
+	})
+}
+
+// HasUsageLogsWith applies the HasEdge predicate on the "usage_logs" edge with a given conditions (other predicates).
+func HasUsageLogsWith(preds ...predicate.UsageLog) predicate.User {
+	return predicate.User(func(s *sql.Selector) {
+		step := newUsageLogsStep()
+		sqlgraph.HasNeighborsWith(s, step, func(s *sql.Selector) {
+			for _, p := range preds {
+				p(s)
+			}
+		})
+	})
+}
+
 // HasUserAllowedGroups applies the HasEdge predicate on the "user_allowed_groups" edge.
 func HasUserAllowedGroups() predicate.User {
 	return predicate.User(func(s *sql.Selector) {