feat: initial commit - Habo habit tracking app

- Complete MVP with Repository Pattern, SQLite storage
- Provider + ChangeNotifier state management
- Navigation 2.0 with deep link support
- Habit CRUD with twoDayRule, notifications, categories
- Backup/Restore via JSON
- Statistics with streak tracking
- Material You theme support
- Biometric lock support
- Desktop widget support
- 27 languages i18n structure
- Comprehensive test suite (87/89 passing)

lib/services/ui_feedback_service.dart

@@ -0,0 +1,48 @@
+import 'package:flutter/material.dart';
+
+class UIFeedbackService {
+  final GlobalKey<ScaffoldMessengerState> _scaffoldKey;
+
+  UIFeedbackService(this._scaffoldKey);
+
+  void showSuccess(String message) {
+    showMessage(message, Colors.green);
+  }
+
+  void showError(String message) {
+    showMessage(message, Colors.red);
+  }
+
+  void showWarning(String message) {
+    showMessage(message, Colors.orange);
+  }
+
+  void showMessage(String message, [Color? color]) {
+    _scaffoldKey.currentState?.showSnackBar(
+      SnackBar(
+        content: Text(message),
+        backgroundColor: color,
+        duration: const Duration(seconds: 2),
+      ),
+    );
+  }
+
+  void showMessageWithAction({
+    required String message,
+    required String actionLabel,
+    required VoidCallback onActionPressed,
+    Color? backgroundColor,
+  }) {
+    _scaffoldKey.currentState?.showSnackBar(
+      SnackBar(
+        content: Text(message),
+        backgroundColor: backgroundColor,
+        action: SnackBarAction(
+          label: actionLabel,
+          onPressed: () => onActionPressed(),
+        ),
+        duration: const Duration(seconds: 4),
+      ),
+    );
+  }
+}