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/account.go

@@ -11,6 +11,7 @@ import (
 	"entgo.io/ent"
 	"entgo.io/ent/dialect/sql"
 	"github.com/Wei-Shaw/sub2api/ent/account"
+	"github.com/Wei-Shaw/sub2api/ent/proxy"
 )
 
 // Account is the model entity for the Account schema.
@@ -70,11 +71,15 @@ type Account struct {
 type AccountEdges struct {
 	// Groups holds the value of the groups edge.
 	Groups []*Group `json:"groups,omitempty"`
+	// Proxy holds the value of the proxy edge.
+	Proxy *Proxy `json:"proxy,omitempty"`
+	// UsageLogs holds the value of the usage_logs edge.
+	UsageLogs []*UsageLog `json:"usage_logs,omitempty"`
 	// AccountGroups holds the value of the account_groups edge.
 	AccountGroups []*AccountGroup `json:"account_groups,omitempty"`
 	// loadedTypes holds the information for reporting if a
 	// type was loaded (or requested) in eager-loading or not.
-	loadedTypes [2]bool
+	loadedTypes [4]bool
 }
 
 // GroupsOrErr returns the Groups value or an error if the edge
@@ -86,10 +91,30 @@ func (e AccountEdges) GroupsOrErr() ([]*Group, error) {
 	return nil, &NotLoadedError{edge: "groups"}
 }
 
+// ProxyOrErr returns the Proxy value or an error if the edge
+// was not loaded in eager-loading, or loaded but was not found.
+func (e AccountEdges) ProxyOrErr() (*Proxy, error) {
+	if e.Proxy != nil {
+		return e.Proxy, nil
+	} else if e.loadedTypes[1] {
+		return nil, &NotFoundError{label: proxy.Label}
+	}
+	return nil, &NotLoadedError{edge: "proxy"}
+}
+
+// UsageLogsOrErr returns the UsageLogs value or an error if the edge
+// was not loaded in eager-loading.
+func (e AccountEdges) UsageLogsOrErr() ([]*UsageLog, error) {
+	if e.loadedTypes[2] {
+		return e.UsageLogs, nil
+	}
+	return nil, &NotLoadedError{edge: "usage_logs"}
+}
+
 // AccountGroupsOrErr returns the AccountGroups value or an error if the edge
 // was not loaded in eager-loading.
 func (e AccountEdges) AccountGroupsOrErr() ([]*AccountGroup, error) {
-	if e.loadedTypes[1] {
+	if e.loadedTypes[3] {
 		return e.AccountGroups, nil
 	}
 	return nil, &NotLoadedError{edge: "account_groups"}
@@ -289,6 +314,16 @@ func (_m *Account) QueryGroups() *GroupQuery {
 	return NewAccountClient(_m.config).QueryGroups(_m)
 }
 
+// QueryProxy queries the "proxy" edge of the Account entity.
+func (_m *Account) QueryProxy() *ProxyQuery {
+	return NewAccountClient(_m.config).QueryProxy(_m)
+}
+
+// QueryUsageLogs queries the "usage_logs" edge of the Account entity.
+func (_m *Account) QueryUsageLogs() *UsageLogQuery {
+	return NewAccountClient(_m.config).QueryUsageLogs(_m)
+}
+
 // QueryAccountGroups queries the "account_groups" edge of the Account entity.
 func (_m *Account) QueryAccountGroups() *AccountGroupQuery {
 	return NewAccountClient(_m.config).QueryAccountGroups(_m)