style: 修复 gofmt 格式化问题

格式化以下测试文件以符合 Go 代码风格规范：
- fixtures_integration_test.go
- user_repo_integration_test.go
- api_key_service_delete_test.go

backend/internal/repository/fixtures_integration_test.go

@@ -390,4 +390,3 @@ func mustBindAccountToGroup(t *testing.T, client *dbent.Client, accountID, group
 		Save(ctx)
 	require.NoError(t, err, "create account_group")
 }
-

backend/internal/repository/user_repo_integration_test.go

@@ -76,8 +76,8 @@ func (s *UserRepoSuite) mustCreateSubscription(userID, groupID int64, mutate fun
 	create := s.client.UserSubscription.Create().
 		SetUserID(userID).
 		SetGroupID(groupID).
-		SetStartsAt(now.Add(-1*time.Hour)).
-		SetExpiresAt(now.Add(24*time.Hour)).
+		SetStartsAt(now.Add(-1 * time.Hour)).
+		SetExpiresAt(now.Add(24 * time.Hour)).
 		SetStatus(service.SubscriptionStatusActive).
 		SetAssignedAt(now).
 		SetNotes("")
@@ -507,4 +507,3 @@ func (s *UserRepoSuite) TestCRUD_And_Filters_And_AtomicUpdates() {
 	s.Require().Len(users, 1, "ListWithFilters len mismatch")
 	s.Require().Equal(user2.ID, users[0].ID, "ListWithFilters result mismatch")
 }
-