Implement relative paths for frontend API and WebSocket connections

- Created `.env.production` file to define relative paths for production deployment.
- Updated frontend API and WebSocket client to use environment variables for dynamic URL handling.
- Enhanced deployment scripts (`deploy-ubuntu.sh`, `start.sh`, `start.bat`) to generate `.env.production` automatically.
- Added `PRODUCTION_URLS.md` for documentation on production URL configuration and troubleshooting.

start.bat

@@ -45,6 +45,11 @@ echo.
 
 REM 4. Сборка frontend
 echo [STEP 4/7] Сборка frontend...
+
+REM Создаем .env.production для production
+echo VITE_API_URL=/api > .env.production
+echo VITE_WS_URL= >> .env.production
+
 call npm run build
 echo [OK] Frontend собран в backend/public
 echo.