Add board navigation and assets

- Introduced new board-related assets in AssetsManager.
- Updated NetworkManager to increase connection and receive timeouts to 20 seconds.
- Added BoardRouteData for navigation to the BoardScreen.
- Updated app routes to include the new board route.
- Modified DesktopNavigationWidget to include a navigation item for the board.
- Added a new string constant for the board label in TendersStrings.

lib/core/network/network_manager.dart

@@ -21,8 +21,8 @@ class NetworkManager {
     : mainDio = Dio(
         BaseOptions(
           baseUrl: AppConfig.apiBaseUrl,
-          connectTimeout: const Duration(seconds: 10),
-          receiveTimeout: const Duration(seconds: 10),
+          connectTimeout: const Duration(seconds: 20),
+          receiveTimeout: const Duration(seconds: 20),
           headers: {
             'Accept': 'application/json',
             'Content-Type': 'application/json',