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>

node_modules/nodemailer/.ncurc.js

@@ -0,0 +1,9 @@
+'use strict';
+
+module.exports = {
+    upgrade: true,
+    reject: [
+        // API changes break existing tests
+        'proxy'
+    ]
+};