feat: Use vitest instead of jest for ESM compatibility

packages/backend/vitest.config.js

@@ -0,0 +1,9 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    environment: 'node',
+    setupFiles: ['./test/setup/global-hooks.js'],
+    globals: true,
+  },
+});