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

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

backend/__tests__/jest.preSetup.js

@@ -0,0 +1,54 @@
+// This file runs before any modules are loaded
+// Mock axios first since couchdbService uses it
+jest.mock('axios', () => ({
+  create: jest.fn(() => ({
+    get: jest.fn().mockResolvedValue({ data: {} }),
+    put: jest.fn().mockResolvedValue({ data: { ok: true } }),
+    post: jest.fn().mockResolvedValue({ data: { ok: true } }),
+    delete: jest.fn().mockResolvedValue({ data: { ok: true } }),
+  })),
+  get: jest.fn().mockResolvedValue({ data: {} }),
+  put: jest.fn().mockResolvedValue({ data: { ok: true } }),
+  post: jest.fn().mockResolvedValue({ data: { ok: true } }),
+  delete: jest.fn().mockResolvedValue({ data: { ok: true } }),
+}));
+
+// Mock CouchDB service at the module level to prevent real service from loading
+jest.mock('../services/couchdbService', () => ({
+  initialize: jest.fn().mockResolvedValue(true),
+  isReady: jest.fn().mockReturnValue(true),
+  isConnected: true,
+  isConnecting: false,
+  create: jest.fn(),
+  getById: jest.fn(),
+  get: jest.fn(),
+  find: jest.fn(),
+  destroy: jest.fn(),
+  delete: jest.fn(),
+  createDocument: jest.fn().mockImplementation((doc) => Promise.resolve({
+    _id: `test_${Date.now()}`,
+    _rev: '1-test',
+    ...doc
+  })),
+  updateDocument: jest.fn().mockImplementation((doc) => Promise.resolve({
+    ...doc,
+    _rev: '2-test'
+  })),
+  deleteDocument: jest.fn().mockResolvedValue(true),
+  findByType: jest.fn().mockResolvedValue([]),
+  findUserById: jest.fn(),
+  findUserByEmail: jest.fn(),
+  update: jest.fn(),
+  updateUserPoints: jest.fn().mockResolvedValue(true),
+  getDocument: jest.fn(),
+  findDocumentById: jest.fn(),
+  bulkDocs: jest.fn().mockResolvedValue([{ ok: true, id: 'test', rev: '1-test' }]),
+  insertMany: jest.fn().mockResolvedValue([]),
+  deleteMany: jest.fn().mockResolvedValue(true),
+  findStreetsByLocation: jest.fn().mockResolvedValue([]),
+  generateId: jest.fn().mockImplementation((type, id) => `${type}_${id}`),
+  extractOriginalId: jest.fn().mockImplementation((prefixedId) => prefixedId.split('_').slice(1).join('_')),
+  validateDocument: jest.fn().mockReturnValue([]),
+  getDB: jest.fn().mockReturnValue({}),
+  shutdown: jest.fn().mockResolvedValue(true),
+}), { virtual: true });