fix: resolve CouchDB test infrastructure issues

- Fix Badge.js model to use correct couchdbService.createDocument() method
- Update Badge.test.js with proper static method testing patterns
- Add missing Post model import in Post.test.js
- Update jest.setup.js with missing mock methods (get, destroy)
- Fix PointTransaction.test.js mock service definition
- Ensure consistent mock patterns across model tests

User and Badge model tests now pass with 40/40 tests working.
Post test import fixed, remaining test issues identified for next iteration.

🤖 Generated with AI Assistant

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

backend/__tests__/models/Post.test.js

@@ -8,11 +8,15 @@ const mockCouchdbService = {
   getDocument: jest.fn(),
   findUserById: jest.fn(),
   update: jest.fn(),
+  create: jest.fn(),
+  getById: jest.fn(),
 };
 
 // Mock the service module
 jest.mock('../../services/couchdbService', () => mockCouchdbService);
 
+const Post = require('../../models/Post');
+
 describe('Post Model', () => {
   beforeEach(() => {
     jest.clearAllMocks();