feat: Use vitest instead of jest for ESM compatibility

packages/backend/test/setup/check-env-file.js

@@ -0,0 +1,12 @@
+import path from 'path';
+import fs from 'fs';
+import { fileURLToPath } from 'url';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const testEnvFile = path.resolve(__dirname, '../../.env.test');
+
+if (!fs.existsSync(testEnvFile)) {
+  throw new Error(
+    'Test environment file (.env.test) not found! You can copy .env-example.test to .env.test and fill it with your own values.'
+  );
+}