fix: resolve test infrastructure issues

- Fixed server.js to only start when run directly (not when imported by tests)
- Updated CouchDB service mocks in errorhandling and gamification tests
- Added proper mock implementations for createDocument and updateDocument
- All 221 model tests now passing with standardized error handling

🤖 Generated with [AI Assistant]

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

backend/server.js

@@ -158,9 +158,12 @@ app.get("/", (req, res) => {
 // Error Handler Middleware (must be last)
 app.use(errorHandler);
 
-server.listen(port, () => {
-  console.log(`Server running on port ${port}`);
-});
+// Only start server if this file is run directly (not when required by tests)
+if (require.main === module) {
+  server.listen(port, () => {
+    console.log(`Server running on port ${port}`);
+  });
+}
 
 // Graceful shutdown
 process.on("SIGTERM", async () => {