fix(apps): consolidate FormzInput validators and fix login screen

- Move FormzInput validators to core/form_inputs/form_inputs.dart
- Fix login_screen.dart syntax error (missing 'class' keyword)
- Remove unused _isLoading field
- Fix unnecessary const keywords
- Update login_cubit and register_cubit imports
- Remove duplicate FormzInput definitions from register_cubit
- Add Toast and Banner UI feedback system
- Remove legacy login/register screens (login_code, login_email, login_password, register_step2)
- Remove unused warning_banner widget
- Update tests for new error messages and DI setup

apps/lib/core/config/env.dart

@@ -1,6 +1,12 @@
+import 'dart:io';
+
 class Env {
   static String get apiUrl {
     const url = String.fromEnvironment('API_URL');
-    return url.isNotEmpty ? url : 'http://localhost:8000';
+    if (url.isNotEmpty) return url;
+    if (Platform.isAndroid) {
+      return 'http://10.0.2.2:5775';
+    }
+    return 'http://localhost:5775';
   }
 }