fix(backend): harden final MVP invariants

backend/internal/models/postgres_integration_test.go

@@ -7,16 +7,15 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"gorm.io/driver/postgres"
+	"gorm.io/gorm"
 )
 
 func TestPostgresPing(t *testing.T) {
-	dsn := os.Getenv("DATABASE_DSN")
-	if dsn == "" {
-		dsn = os.Getenv("DATABASE_URL")
-	}
-	require.NotEmpty(t, dsn, "DATABASE_DSN or DATABASE_URL is required for integration tests")
+	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 := Open(dsn)
+	database, err := gorm.Open(postgres.Open(dsn), &gorm.Config{TranslateError: true})
 	require.NoError(t, err)
 	sqlDB, err := database.DB()
 	require.NoError(t, err)