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__/socketio.test.js

@@ -1,7 +1,7 @@
 const request = require("supertest");
 const socketIoClient = require("socket.io-client");
 const jwt = require("jsonwebtoken");
-const app = require("../server");
+const { app, server, io } = require("../server");
 const User = require("../models/User");
 const Event = require("../models/Event");
 const Post = require("../models/Post");
@@ -15,9 +15,10 @@ describe("Socket.IO Real-time Features", () => {
   let authToken;
 
   beforeAll(async () => {
-    // Start server
-    server = app.listen(0); // Use random port
-    io = app.get("io");
+    // Start server if not already started
+    if (!server.listening) {
+      server.listen(0); // Use random port
+    }
 
     // Create test user
     testUser = await User.create({