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/usersubscription/where.go

@@ -65,6 +65,11 @@ func UpdatedAt(v time.Time) predicate.UserSubscription {
 	return predicate.UserSubscription(sql.FieldEQ(FieldUpdatedAt, v))
 }
 
+// DeletedAt applies equality check predicate on the "deleted_at" field. It's identical to DeletedAtEQ.
+func DeletedAt(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldEQ(FieldDeletedAt, v))
+}
+
 // UserID applies equality check predicate on the "user_id" field. It's identical to UserIDEQ.
 func UserID(v int64) predicate.UserSubscription {
 	return predicate.UserSubscription(sql.FieldEQ(FieldUserID, v))
@@ -215,6 +220,56 @@ func UpdatedAtLTE(v time.Time) predicate.UserSubscription {
 	return predicate.UserSubscription(sql.FieldLTE(FieldUpdatedAt, v))
 }
 
+// DeletedAtEQ applies the EQ predicate on the "deleted_at" field.
+func DeletedAtEQ(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldEQ(FieldDeletedAt, v))
+}
+
+// DeletedAtNEQ applies the NEQ predicate on the "deleted_at" field.
+func DeletedAtNEQ(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldNEQ(FieldDeletedAt, v))
+}
+
+// DeletedAtIn applies the In predicate on the "deleted_at" field.
+func DeletedAtIn(vs ...time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldIn(FieldDeletedAt, vs...))
+}
+
+// DeletedAtNotIn applies the NotIn predicate on the "deleted_at" field.
+func DeletedAtNotIn(vs ...time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldNotIn(FieldDeletedAt, vs...))
+}
+
+// DeletedAtGT applies the GT predicate on the "deleted_at" field.
+func DeletedAtGT(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldGT(FieldDeletedAt, v))
+}
+
+// DeletedAtGTE applies the GTE predicate on the "deleted_at" field.
+func DeletedAtGTE(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldGTE(FieldDeletedAt, v))
+}
+
+// DeletedAtLT applies the LT predicate on the "deleted_at" field.
+func DeletedAtLT(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldLT(FieldDeletedAt, v))
+}
+
+// DeletedAtLTE applies the LTE predicate on the "deleted_at" field.
+func DeletedAtLTE(v time.Time) predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldLTE(FieldDeletedAt, v))
+}
+
+// DeletedAtIsNil applies the IsNil predicate on the "deleted_at" field.
+func DeletedAtIsNil() predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldIsNull(FieldDeletedAt))
+}
+
+// DeletedAtNotNil applies the NotNil predicate on the "deleted_at" field.
+func DeletedAtNotNil() predicate.UserSubscription {
+	return predicate.UserSubscription(sql.FieldNotNull(FieldDeletedAt))
+}
+
 // UserIDEQ applies the EQ predicate on the "user_id" field.
 func UserIDEQ(v int64) predicate.UserSubscription {
 	return predicate.UserSubscription(sql.FieldEQ(FieldUserID, v))
@@ -884,6 +939,29 @@ func HasAssignedByUserWith(preds ...predicate.User) predicate.UserSubscription {
 	})
 }
 
+// HasUsageLogs applies the HasEdge predicate on the "usage_logs" edge.
+func HasUsageLogs() predicate.UserSubscription {
+	return predicate.UserSubscription(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.UserSubscription {
+	return predicate.UserSubscription(func(s *sql.Selector) {
+		step := newUsageLogsStep()
+		sqlgraph.HasNeighborsWith(s, step, func(s *sql.Selector) {
+			for _, p := range preds {
+				p(s)
+			}
+		})
+	})
+}
+
 // And groups predicates with the AND operator between them.
 func And(predicates ...predicate.UserSubscription) predicate.UserSubscription {
 	return predicate.UserSubscription(sql.AndPredicates(predicates...))