Refactored notification utilities for a more modern, reusable notification system and added info/success/error notifications to the background removal (matting) workflow. Removed the custom error dialog in favor of notifications, and exposed all notification types for debugging. Updated imports and cleaned up notification-related code.
Adds a modern, type-based notification UI with support for success, error, info, warning, and alert styles, including a new showAlertNotification function. CanvasState now auto-corrects the node_id widget before saving state and notifies the user if a correction occurs. CanvasView centering logic now uses the actual canvas container for more accurate viewport adjustments.
Extracted image upload, mask processing, notification, and preview update logic into dedicated utility modules. Updated MaskEditorIntegration and SAMDetectorIntegration to use these new utilities, reducing code duplication and improving maintainability.
