fix: update model test mocking for CouchDB compatibility

- Replace jest.mock with proper hoisted mocks for Jest compatibility
- Add missing CouchDB service methods to mocks (findUserById, create, getById, update)
- Update Post model tests to work with static class methods instead of constructor validation
- Fix mock service references throughout all model test files

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

backend/__tests__/models/User.test.js

@@ -1,17 +1,29 @@
 const User = require('../../models/User');
-const couchdbService = require('../../services/couchdbService');
 
 // Mock CouchDB service for testing
-jest.mock('../../services/couchdbService');
+const mockCouchdbService = {
+  findUserByEmail: jest.fn(),
+  findUserById: jest.fn(),
+  createDocument: jest.fn(),
+  updateDocument: jest.fn(),
+  findByType: jest.fn(),
+  deleteDocument: jest.fn(),
+  initialize: jest.fn(),
+  isReady: jest.fn().mockReturnValue(true),
+  shutdown: jest.fn()
+};
+
+// Mock the service module
+jest.mock('../../services/couchdbService', () => mockCouchdbService);
 
 describe('User Model', () => {
   beforeEach(() => {
     jest.clearAllMocks();
     // Reset all mocks to ensure clean state
-    couchdbService.findUserByEmail.mockReset();
-    couchdbService.findUserById.mockReset();
-    couchdbService.createDocument.mockReset();
-    couchdbService.updateDocument.mockReset();
+    mockCouchdbService.findUserByEmail.mockReset();
+    mockCouchdbService.findUserById.mockReset();
+    mockCouchdbService.createDocument.mockReset();
+    mockCouchdbService.updateDocument.mockReset();
   });
 
   describe('Schema Validation', () => {