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.go

@@ -59,11 +59,13 @@ type UserEdges struct {
 	AssignedSubscriptions []*UserSubscription `json:"assigned_subscriptions,omitempty"`
 	// AllowedGroups holds the value of the allowed_groups edge.
 	AllowedGroups []*Group `json:"allowed_groups,omitempty"`
+	// UsageLogs holds the value of the usage_logs edge.
+	UsageLogs []*UsageLog `json:"usage_logs,omitempty"`
 	// UserAllowedGroups holds the value of the user_allowed_groups edge.
 	UserAllowedGroups []*UserAllowedGroup `json:"user_allowed_groups,omitempty"`
 	// loadedTypes holds the information for reporting if a
 	// type was loaded (or requested) in eager-loading or not.
-	loadedTypes [6]bool
+	loadedTypes [7]bool
 }
 
 // APIKeysOrErr returns the APIKeys value or an error if the edge
@@ -111,10 +113,19 @@ func (e UserEdges) AllowedGroupsOrErr() ([]*Group, error) {
 	return nil, &NotLoadedError{edge: "allowed_groups"}
 }
 
+// UsageLogsOrErr returns the UsageLogs value or an error if the edge
+// was not loaded in eager-loading.
+func (e UserEdges) UsageLogsOrErr() ([]*UsageLog, error) {
+	if e.loadedTypes[5] {
+		return e.UsageLogs, nil
+	}
+	return nil, &NotLoadedError{edge: "usage_logs"}
+}
+
 // UserAllowedGroupsOrErr returns the UserAllowedGroups value or an error if the edge
 // was not loaded in eager-loading.
 func (e UserEdges) UserAllowedGroupsOrErr() ([]*UserAllowedGroup, error) {
-	if e.loadedTypes[5] {
+	if e.loadedTypes[6] {
 		return e.UserAllowedGroups, nil
 	}
 	return nil, &NotLoadedError{edge: "user_allowed_groups"}
@@ -265,6 +276,11 @@ func (_m *User) QueryAllowedGroups() *GroupQuery {
 	return NewUserClient(_m.config).QueryAllowedGroups(_m)
 }
 
+// QueryUsageLogs queries the "usage_logs" edge of the User entity.
+func (_m *User) QueryUsageLogs() *UsageLogQuery {
+	return NewUserClient(_m.config).QueryUsageLogs(_m)
+}
+
 // QueryUserAllowedGroups queries the "user_allowed_groups" edge of the User entity.
 func (_m *User) QueryUserAllowedGroups() *UserAllowedGroupQuery {
 	return NewUserClient(_m.config).QueryUserAllowedGroups(_m)