fix: resolve CouchDB connection issues in backend tests

- Add jest.preSetup.js to mock modules before loading
- Skip CouchDB initialization during test environment
- Update browserslist data to fix deprecation warnings
- Improve error handling test infrastructure
- Fix fs.F_OK deprecation warning via dependency update

🤖 Generated with [AI Assistant]

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

backend/jest.config.js

@@ -20,6 +20,7 @@ module.exports = {
       statements: 70
     }
   },
+  setupFiles: ['<rootDir>/__tests__/jest.preSetup.js'],
   setupFilesAfterEnv: ['<rootDir>/__tests__/jest.setup.js'],
   testTimeout: 30000,
   verbose: true