fix(backend): secure production startup and migrations

backend/internal/seed/demo_postgres_test.go

@@ -5,17 +5,16 @@ package seed
 import (
 	"context"
 	"fmt"
-	"os"
 	"sync"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/require"
 	"golang.org/x/crypto/bcrypt"
-	"gorm.io/driver/postgres"
 	"gorm.io/gorm"
 	"gorm.io/gorm/logger"
 	"senlinai-agent/backend/internal/models"
+	"senlinai-agent/backend/internal/testutil"
 )
 
 type demoSeedRunContextKey struct{}
@@ -28,13 +27,10 @@ const (
 )
 
 func TestPostgresDemoSeedSerializesConcurrentRunsForSameOwner(t *testing.T) {
-	dsn := os.Getenv("TEST_DATABASE_URL")
-	require.NotEmpty(t, dsn, "TEST_DATABASE_URL is required for integration tests and must point to an isolated database")
-	database, err := gorm.Open(postgres.Open(dsn), &gorm.Config{
+	database := testutil.OpenIsolatedPostgres(t, &gorm.Config{
 		TranslateError: true,
 		Logger:         logger.Default.LogMode(logger.Silent),
 	})
-	require.NoError(t, err)
 	require.NoError(t, models.AutoMigrate(database))
 
 	suffix := fmt.Sprint(time.Now().UnixNano())