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>

backend/__tests__/gamification.test.js

@@ -24,13 +24,14 @@ jest.mock('../services/couchdbService', () => ({
         type: 'user',
         name: 'Test User',
         email: 'test@example.com',
+        password: 'hashedpassword',
         points: 100,
         stats: {
           streetsAdopted: 1,
           tasksCompleted: 1,
           postsCreated: 1,
           eventsParticipated: 1,
-          badgesEarnn: 1
+          badgesEarned: 1
         }
       };
     }
@@ -39,6 +40,7 @@ jest.mock('../services/couchdbService', () => ({
   findUserByEmail: jest.fn(),
   update: jest.fn(),
   getDocument: jest.fn(),
+  shutdown: jest.fn().mockResolvedValue(true),
 }));
 
 const request = require("supertest");