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/proxy.go

@@ -36,10 +36,31 @@ type Proxy struct {
 	// Password holds the value of the "password" field.
 	Password *string `json:"password,omitempty"`
 	// Status holds the value of the "status" field.
-	Status       string `json:"status,omitempty"`
+	Status string `json:"status,omitempty"`
+	// Edges holds the relations/edges for other nodes in the graph.
+	// The values are being populated by the ProxyQuery when eager-loading is set.
+	Edges        ProxyEdges `json:"edges"`
 	selectValues sql.SelectValues
 }
 
+// ProxyEdges holds the relations/edges for other nodes in the graph.
+type ProxyEdges struct {
+	// Accounts holds the value of the accounts edge.
+	Accounts []*Account `json:"accounts,omitempty"`
+	// loadedTypes holds the information for reporting if a
+	// type was loaded (or requested) in eager-loading or not.
+	loadedTypes [1]bool
+}
+
+// AccountsOrErr returns the Accounts value or an error if the edge
+// was not loaded in eager-loading.
+func (e ProxyEdges) AccountsOrErr() ([]*Account, error) {
+	if e.loadedTypes[0] {
+		return e.Accounts, nil
+	}
+	return nil, &NotLoadedError{edge: "accounts"}
+}
+
 // scanValues returns the types for scanning values from sql.Rows.
 func (*Proxy) scanValues(columns []string) ([]any, error) {
 	values := make([]any, len(columns))
@@ -148,6 +169,11 @@ func (_m *Proxy) Value(name string) (ent.Value, error) {
 	return _m.selectValues.Get(name)
 }
 
+// QueryAccounts queries the "accounts" edge of the Proxy entity.
+func (_m *Proxy) QueryAccounts() *AccountQuery {
+	return NewProxyClient(_m.config).QueryAccounts(_m)
+}
+
 // Update returns a builder for updating this Proxy.
 // Note that you need to call Proxy.Unwrap() before calling this method if this Proxy
 // was returned from a transaction, and the transaction was committed or rolled back.