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/internal/repository/soft_delete_ent_integration_test.go

@@ -7,10 +7,12 @@ import (
 	"fmt"
 	"strings"
 	"testing"
+	"time"
 
 	dbent "github.com/Wei-Shaw/sub2api/ent"
 	"github.com/Wei-Shaw/sub2api/ent/apikey"
 	"github.com/Wei-Shaw/sub2api/ent/schema/mixins"
+	"github.com/Wei-Shaw/sub2api/ent/usersubscription"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 	"github.com/stretchr/testify/require"
 )
@@ -111,3 +113,104 @@ func TestEntSoftDelete_ApiKey_HardDeleteViaSkipSoftDelete(t *testing.T) {
 		Only(mixins.SkipSoftDelete(ctx))
 	require.True(t, dbent.IsNotFound(err), "expected row to be hard deleted")
 }
+
+// --- UserSubscription 软删除测试 ---
+
+func createEntGroup(t *testing.T, ctx context.Context, client *dbent.Client, name string) *dbent.Group {
+	t.Helper()
+
+	g, err := client.Group.Create().
+		SetName(name).
+		SetStatus(service.StatusActive).
+		Save(ctx)
+	require.NoError(t, err, "create ent group")
+	return g
+}
+
+func TestEntSoftDelete_UserSubscription_DefaultFilterAndSkip(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+
+	u := createEntUser(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-user")+"@example.com")
+	g := createEntGroup(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-group"))
+
+	repo := NewUserSubscriptionRepository(client)
+	sub := &service.UserSubscription{
+		UserID:    u.ID,
+		GroupID:   g.ID,
+		Status:    service.SubscriptionStatusActive,
+		ExpiresAt: time.Now().Add(24 * time.Hour),
+	}
+	require.NoError(t, repo.Create(ctx, sub), "create user subscription")
+
+	require.NoError(t, repo.Delete(ctx, sub.ID), "soft delete user subscription")
+
+	_, err := repo.GetByID(ctx, sub.ID)
+	require.Error(t, err, "deleted rows should be hidden by default")
+
+	_, err = client.UserSubscription.Query().Where(usersubscription.IDEQ(sub.ID)).Only(ctx)
+	require.Error(t, err, "default ent query should not see soft-deleted rows")
+	require.True(t, dbent.IsNotFound(err), "expected ent not-found after default soft delete filter")
+
+	got, err := client.UserSubscription.Query().
+		Where(usersubscription.IDEQ(sub.ID)).
+		Only(mixins.SkipSoftDelete(ctx))
+	require.NoError(t, err, "SkipSoftDelete should include soft-deleted rows")
+	require.NotNil(t, got.DeletedAt, "deleted_at should be set after soft delete")
+}
+
+func TestEntSoftDelete_UserSubscription_DeleteIdempotent(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+
+	u := createEntUser(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-user2")+"@example.com")
+	g := createEntGroup(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-group2"))
+
+	repo := NewUserSubscriptionRepository(client)
+	sub := &service.UserSubscription{
+		UserID:    u.ID,
+		GroupID:   g.ID,
+		Status:    service.SubscriptionStatusActive,
+		ExpiresAt: time.Now().Add(24 * time.Hour),
+	}
+	require.NoError(t, repo.Create(ctx, sub), "create user subscription")
+
+	require.NoError(t, repo.Delete(ctx, sub.ID), "first delete")
+	require.NoError(t, repo.Delete(ctx, sub.ID), "second delete should be idempotent")
+}
+
+func TestEntSoftDelete_UserSubscription_ListExcludesDeleted(t *testing.T) {
+	ctx := context.Background()
+	client := testEntClient(t)
+
+	u := createEntUser(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-user3")+"@example.com")
+	g1 := createEntGroup(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-group3a"))
+	g2 := createEntGroup(t, ctx, client, uniqueSoftDeleteValue(t, "sd-sub-group3b"))
+
+	repo := NewUserSubscriptionRepository(client)
+
+	sub1 := &service.UserSubscription{
+		UserID:    u.ID,
+		GroupID:   g1.ID,
+		Status:    service.SubscriptionStatusActive,
+		ExpiresAt: time.Now().Add(24 * time.Hour),
+	}
+	require.NoError(t, repo.Create(ctx, sub1), "create subscription 1")
+
+	sub2 := &service.UserSubscription{
+		UserID:    u.ID,
+		GroupID:   g2.ID,
+		Status:    service.SubscriptionStatusActive,
+		ExpiresAt: time.Now().Add(24 * time.Hour),
+	}
+	require.NoError(t, repo.Create(ctx, sub2), "create subscription 2")
+
+	// 软删除 sub1
+	require.NoError(t, repo.Delete(ctx, sub1.ID), "soft delete subscription 1")
+
+	// ListByUserID 应只返回未删除的订阅
+	subs, err := repo.ListByUserID(ctx, u.ID)
+	require.NoError(t, err, "ListByUserID")
+	require.Len(t, subs, 1, "should only return non-deleted subscriptions")
+	require.Equal(t, sub2.ID, subs[0].ID, "expected sub2 to be returned")
+}