Fix Fuego network default RPC port

- Update defaultRpcPort from 28180 to 18180 (correct Fuego network default)
- Update settings screen hint text to show correct port format
- Align with actual Fuego network configuration

Author: ColinRitman

lib/screens/settings/settings_screen.dart

@@ -240,7 +240,7 @@ class _SettingsScreenState extends State<SettingsScreen> {
                   TextField(
                     controller: customNodeController,
                     decoration: InputDecoration(
-                      hintText: 'node.example.com:28180',
+                      hintText: 'node.example.com:18180',
                       hintStyle: TextStyle(color: AppTheme.textSecondary.withOpacity(0.5)),
                       enabledBorder: OutlineInputBorder(
                         borderSide: BorderSide(color: AppTheme.textSecondary.withOpacity(0.3)),

lib/services/fuego_rpc_service.dart

@@ -9,7 +9,7 @@ class FuegoRPCService {
   String _baseUrl;
   final String? _password;
 
-  static const int defaultRpcPort = 28180;
+  static const int defaultRpcPort = 18180;
   static const int defaultWalletPort = 8070;
 
   // Default remote Fuego nodes (public community nodes)