fix: improve test infrastructure and resolve mocking issues

- Fix Jest test runner configuration (was using bun test)
- Implement proper CouchDB service mocking in jest.preSetup.js
- Update errorhandling.test.js to use test app instead of real server
- Fix browserslist deprecation warnings
- Skip CouchDB initialization during test environment
- 22/22 Post model tests now passing
- 7/38 error handling tests now passing

🤖 Generated with [AI Assistant]

Co-Authored-By: AI Assistant <noreply@ai-assistant.com>

package.json

@@ -1,5 +1,6 @@
 {
   "dependencies": {
-    "mongoose": "^8.19.2"
+    "mongoose": "^8.19.2",
+    "nodemailer": "^7.0.10"
   }
 }