refactor: Update GUI components and integrate new palette widget

- Removed references to the old `EnhancedPaletteEditor` and replaced it with the new `PaletteWidget` across various files, including canvas and context menu implementations.
- Updated CMake configurations to include the new `palette_widget` source files, ensuring proper integration into the build system.
- Refactored GUI code to enhance modularity and maintainability, improving the overall user experience in palette management and editing functionalities.
- Introduced new UI components for background rendering and editor selection dialogs, enhancing the application's graphical interface.

src/app/gui/canvas.cc

@@ -67,7 +67,7 @@ void Canvas::InitializeDefaults() {
   selection_.Clear();
 
   // Initialize palette editor
-  palette_editor_ = std::make_unique<EnhancedPaletteEditor>();
+  palette_editor_ = std::make_unique<PaletteWidget>();
 
   // Initialize interaction handler
   interaction_handler_.Initialize(canvas_id_);
@@ -1744,7 +1744,7 @@ void Canvas::ShowAdvancedCanvasProperties() {
   }
 }
 
-// Old ShowPaletteManager method removed - now handled by EnhancedPaletteEditor
+// Old ShowPaletteManager method removed - now handled by PaletteWidget
 
 void Canvas::ShowScalingControls() {
   // Use the new modal system if available