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/toast/index.dart

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+export 'toast.dart';
+export 'toast_type.dart';
+export 'toast_type_config.dart';

apps/lib/shared/widgets/toast/toast.dart

@@ -0,0 +1,128 @@
+import 'package:flutter/material.dart';
+import '../../../core/theme/design_tokens.dart';
+import 'toast_type.dart';
+import 'toast_type_config.dart';
+
+class Toast {
+  static void show(
+    BuildContext context,
+    String message, {
+    ToastType type = ToastType.info,
+    Duration duration = const Duration(seconds: 2),
+  }) {
+    final overlay = Overlay.of(context);
+    late OverlayEntry entry;
+
+    entry = OverlayEntry(
+      builder: (context) => _ToastWidget(
+        message: message,
+        type: type,
+        duration: duration,
+        onDismiss: () => entry.remove(),
+      ),
+    );
+
+    overlay.insert(entry);
+  }
+}
+
+class _ToastWidget extends StatefulWidget {
+  final String message;
+  final ToastType type;
+  final Duration duration;
+  final VoidCallback onDismiss;
+
+  const _ToastWidget({
+    required this.message,
+    required this.type,
+    required this.duration,
+    required this.onDismiss,
+  });
+
+  @override
+  State<_ToastWidget> createState() => _ToastWidgetState();
+}
+
+class _ToastWidgetState extends State<_ToastWidget>
+    with SingleTickerProviderStateMixin {
+  late AnimationController _controller;
+  late Animation<Offset> _slideAnimation;
+  late Animation<double> _fadeAnimation;
+
+  @override
+  void initState() {
+    super.initState();
+    _controller = AnimationController(
+      duration: const Duration(milliseconds: 250),
+      vsync: this,
+    );
+
+    _slideAnimation = Tween<Offset>(
+      begin: const Offset(0, -1),
+      end: Offset.zero,
+    ).animate(CurvedAnimation(parent: _controller, curve: Curves.easeOut));
+
+    _fadeAnimation = Tween<double>(begin: 0, end: 1).animate(_controller);
+
+    _controller.forward();
+
+    Future.delayed(widget.duration, _dismiss);
+  }
+
+  void _dismiss() {
+    if (!mounted) return;
+    _controller.reverse().then((_) => widget.onDismiss());
+  }
+
+  @override
+  void dispose() {
+    _controller.dispose();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    final config = ToastTypeConfig.fromType(widget.type);
+
+    return Positioned(
+      top: MediaQuery.of(context).padding.top + 16,
+      left: 16,
+      right: 16,
+      child: SlideTransition(
+        position: _slideAnimation,
+        child: FadeTransition(
+          opacity: _fadeAnimation,
+          child: Material(
+            color: Colors.transparent,
+            child: Container(
+              padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 12),
+              decoration: BoxDecoration(
+                color: config.backgroundColor,
+                borderRadius: BorderRadius.circular(AppRadius.md),
+                boxShadow: [
+                  BoxShadow(
+                    color: Colors.black.withValues(alpha: 0.1),
+                    blurRadius: 8,
+                    offset: const Offset(0, 2),
+                  ),
+                ],
+              ),
+              child: Row(
+                children: [
+                  Icon(config.icon, size: 20, color: config.iconColor),
+                  const SizedBox(width: 12),
+                  Expanded(
+                    child: Text(
+                      widget.message,
+                      style: TextStyle(fontSize: 14, color: config.textColor),
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}

apps/lib/shared/widgets/toast/toast_type.dart

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+enum ToastType { info, success, warning, error }

apps/lib/shared/widgets/toast/toast_type_config.dart

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+import 'package:flutter/material.dart';
+import 'toast_type.dart';
+
+class ToastTypeConfig {
+  final Color backgroundColor;
+  final Color iconColor;
+  final Color textColor;
+  final IconData icon;
+
+  const ToastTypeConfig({
+    required this.backgroundColor,
+    required this.iconColor,
+    required this.textColor,
+    required this.icon,
+  });
+
+  static ToastTypeConfig fromType(ToastType type) => switch (type) {
+    ToastType.success => const ToastTypeConfig(
+      backgroundColor: Color(0xFFECFDF5),
+      iconColor: Color(0xFF10B981),
+      textColor: Color(0xFF065F46),
+      icon: Icons.check_circle_outline,
+    ),
+    ToastType.warning => const ToastTypeConfig(
+      backgroundColor: Color(0xFFFFFBEB),
+      iconColor: Color(0xFFF59E0B),
+      textColor: Color(0xFF92400E),
+      icon: Icons.warning_amber_rounded,
+    ),
+    ToastType.error => const ToastTypeConfig(
+      backgroundColor: Color(0xFFFEF2F2),
+      iconColor: Color(0xFFEF4444),
+      textColor: Color(0xFF991B1B),
+      icon: Icons.error_outline,
+    ),
+    ToastType.info => const ToastTypeConfig(
+      backgroundColor: Color(0xFFEFF6FF),
+      iconColor: Color(0xFF3B82F6),
+      textColor: Color(0xFF1E40AF),
+      icon: Icons.info_outline,
+    ),
+  };
+}