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/group/where.go

@@ -120,6 +120,11 @@ func MonthlyLimitUsd(v float64) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldMonthlyLimitUsd, v))
 }
 
+// DefaultValidityDays applies equality check predicate on the "default_validity_days" field. It's identical to DefaultValidityDaysEQ.
+func DefaultValidityDays(v int) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldDefaultValidityDays, v))
+}
+
 // CreatedAtEQ applies the EQ predicate on the "created_at" field.
 func CreatedAtEQ(v time.Time) predicate.Group {
 	return predicate.Group(sql.FieldEQ(FieldCreatedAt, v))
@@ -785,6 +790,46 @@ func MonthlyLimitUsdNotNil() predicate.Group {
 	return predicate.Group(sql.FieldNotNull(FieldMonthlyLimitUsd))
 }
 
+// DefaultValidityDaysEQ applies the EQ predicate on the "default_validity_days" field.
+func DefaultValidityDaysEQ(v int) predicate.Group {
+	return predicate.Group(sql.FieldEQ(FieldDefaultValidityDays, v))
+}
+
+// DefaultValidityDaysNEQ applies the NEQ predicate on the "default_validity_days" field.
+func DefaultValidityDaysNEQ(v int) predicate.Group {
+	return predicate.Group(sql.FieldNEQ(FieldDefaultValidityDays, v))
+}
+
+// DefaultValidityDaysIn applies the In predicate on the "default_validity_days" field.
+func DefaultValidityDaysIn(vs ...int) predicate.Group {
+	return predicate.Group(sql.FieldIn(FieldDefaultValidityDays, vs...))
+}
+
+// DefaultValidityDaysNotIn applies the NotIn predicate on the "default_validity_days" field.
+func DefaultValidityDaysNotIn(vs ...int) predicate.Group {
+	return predicate.Group(sql.FieldNotIn(FieldDefaultValidityDays, vs...))
+}
+
+// DefaultValidityDaysGT applies the GT predicate on the "default_validity_days" field.
+func DefaultValidityDaysGT(v int) predicate.Group {
+	return predicate.Group(sql.FieldGT(FieldDefaultValidityDays, v))
+}
+
+// DefaultValidityDaysGTE applies the GTE predicate on the "default_validity_days" field.
+func DefaultValidityDaysGTE(v int) predicate.Group {
+	return predicate.Group(sql.FieldGTE(FieldDefaultValidityDays, v))
+}
+
+// DefaultValidityDaysLT applies the LT predicate on the "default_validity_days" field.
+func DefaultValidityDaysLT(v int) predicate.Group {
+	return predicate.Group(sql.FieldLT(FieldDefaultValidityDays, v))
+}
+
+// DefaultValidityDaysLTE applies the LTE predicate on the "default_validity_days" field.
+func DefaultValidityDaysLTE(v int) predicate.Group {
+	return predicate.Group(sql.FieldLTE(FieldDefaultValidityDays, v))
+}
+
 // HasAPIKeys applies the HasEdge predicate on the "api_keys" edge.
 func HasAPIKeys() predicate.Group {
 	return predicate.Group(func(s *sql.Selector) {
@@ -854,6 +899,29 @@ func HasSubscriptionsWith(preds ...predicate.UserSubscription) predicate.Group {
 	})
 }
 
+// HasUsageLogs applies the HasEdge predicate on the "usage_logs" edge.
+func HasUsageLogs() predicate.Group {
+	return predicate.Group(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.Group {
+	return predicate.Group(func(s *sql.Selector) {
+		step := newUsageLogsStep()
+		sqlgraph.HasNeighborsWith(s, step, func(s *sql.Selector) {
+			for _, p := range preds {
+				p(s)
+			}
+		})
+	})
+}
+
 // HasAccounts applies the HasEdge predicate on the "accounts" edge.
 func HasAccounts() predicate.Group {
 	return predicate.Group(func(s *sql.Selector) {