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/shared/widgets/banner/app_banner.dart

@@ -0,0 +1,45 @@
+import 'package:flutter/material.dart';
+import '../../../core/theme/design_tokens.dart';
+import '../toast/toast_type.dart';
+import '../toast/toast_type_config.dart' show ToastTypeConfig;
+
+class AppBanner extends StatelessWidget {
+  final String message;
+  final ToastType type;
+  final bool visible;
+
+  const AppBanner({
+    super.key,
+    required this.message,
+    this.type = ToastType.warning,
+    this.visible = true,
+  });
+
+  @override
+  Widget build(BuildContext context) {
+    if (!visible) return const SizedBox.shrink();
+
+    final config = ToastTypeConfig.fromType(type);
+
+    return Container(
+      width: double.infinity,
+      padding: const EdgeInsets.symmetric(horizontal: 12, vertical: 10),
+      decoration: BoxDecoration(
+        color: config.backgroundColor,
+        borderRadius: BorderRadius.circular(AppRadius.sm),
+      ),
+      child: Row(
+        children: [
+          Icon(config.icon, size: 16, color: config.iconColor),
+          const SizedBox(width: 8),
+          Expanded(
+            child: Text(
+              message,
+              style: TextStyle(fontSize: 13, color: config.textColor),
+            ),
+          ),
+        ],
+      ),
+    );
+  }
+}