feat(frontend): make baseUrl dynamic for external network access and clear default login inputs

FinlyticApp/lib/core/network/api_client.dart

@@ -1,4 +1,5 @@
 import 'package:dio/dio.dart';
+import 'package:flutter/foundation.dart';
 import '../services/secure_storage_service.dart';
 
 /// Central HTTP ApiClient backed by Dio with automatic 401 Unauthorized handling.
@@ -7,7 +8,15 @@ class ApiClient {
   late final Dio _dio;
   Function()? onUnauthorized;
 
-  static const String baseUrl = 'http://localhost:5000';
+  static String get baseUrl {
+    if (kIsWeb) {
+      final origin = Uri.base.origin;
+      if (origin.isNotEmpty && !origin.contains('null') && !origin.startsWith('file:')) {
+        return origin;
+      }
+    }
+    return const String.fromEnvironment('BACKEND_URL', defaultValue: 'http://localhost:5000');
+  }
 
   ApiClient(this._storageService) {
     _dio = Dio(

FinlyticApp/lib/core/network/signalr_service.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'package:finlytic_app/core/network/api_client.dart';
 import 'package:flutter/foundation.dart';
 import 'package:signalr_core/signalr_core.dart';
 import '../services/secure_storage_service.dart';
@@ -21,7 +22,7 @@ class SignalRService extends ChangeNotifier {
   Stream<List<Map<String, dynamic>>> get healthStream => _healthController.stream;
   Stream<Map<String, dynamic>> get favoritePricesStream => _favoritePricesController.stream;
 
-  static const String baseUrl = 'http://localhost:5000';
+  static String get baseUrl => ApiClient.baseUrl;
 
   SignalRService(this.storageService);