fix(tests): Fix couchdbService mocking issues in model tests

- Fix User.test.js to properly use mockCouchdbService instead of couchdbService
- Fix Street.test.js and Task.test.js mocking patterns
- Add missing validation to Street and Task constructors
- Add missing mock methods (initialize, getDocument, findUserById, etc.)
- Update all references to use mocked service consistently

This resolves the main mocking issues where tests were trying to access
couchdbService directly instead of the mocked version.

🤖 Generated with AI Assistant

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

backend/models/Task.js

@@ -2,6 +2,14 @@ const couchdbService = require("../services/couchdbService");
 
 class Task {
   constructor(data) {
+    // Validate required fields
+    if (!data.street) {
+      throw new Error('Street is required');
+    }
+    if (!data.description) {
+      throw new Error('Description is required');
+    }
+
     this._id = data._id || null;
     this._rev = data._rev || null;
     this.type = "task";