Improves all-day drag-and-drop conversion

Refactors drag-to-all-day functionality to apply CSS styling and reposition the existing drag clone within the all-day container, rather than creating a new event element.

Centralizes all-day container creation in HeaderManager. Introduces `drag:mouseleave-header` to handle transitions from all-day back to timed events.

Ensures consistent styling and robust cleanup of drag clones for a smoother user experience.

src/managers/DragDropManager.ts

@@ -260,6 +260,7 @@ export class DragDropManager {
 
       // Clean up drag state first
       this.cleanupDragState();
+     
 
       // Only emit drag:end if drag was actually started
       if (isDragStarted) {
@@ -286,6 +287,9 @@ export class DragDropManager {
           target: dropTarget
         };
         this.eventBus.emit('drag:end', dragEndPayload);
+
+        draggedElement.remove();
+
       } else {
         // This was just a click - emit click event instead
         this.eventBus.emit('event:click', {
@@ -295,6 +299,12 @@ export class DragDropManager {
       }
     }
   }
+  // Add a cleanup method that finds and removes ALL clones
+  private cleanupAllClones(): void {
+    // Remove clones from all possible locations
+    const allClones = document.querySelectorAll('[data-event-id^="clone"]');
+    allClones.forEach(clone => clone.remove());
+  }
 
   /**
    * Consolidated position calculation method using PositionUtils