Improves event drag and drop highlighting

Enhances the visual feedback during and after event drag and drop operations in the calendar.

- Preserves the full opacity of the dragged event clone during the drag operation for better visibility.
- Applies a highlight class to the event after it's dropped to visually indicate the new location.
- Adds specific styling for the highlighted state based on event type.

src/renderers/AllDayEventRenderer.ts

@@ -79,6 +79,9 @@ export class AllDayEventRenderer {
     const dayEvent = SwpAllDayEventElement.fromCalendarEvent(event);
     dayEvent.applyGridPositioning(layout.row, layout.startColumn, layout.endColumn);
 
+    // Apply highlight class to show events with highlight color
+    dayEvent.classList.add('highlight');
+
     container.appendChild(dayEvent);
   }