Improves header drag-and-drop event handling

Enhances drag leave logic for more precise event tracking
- Adds conditional cleanup for grid-to-header drag events
- Updates drag state management during column transitions
- Prevents premature ghost element removal

src/v2/features/headerdrawer/HeaderDrawerRenderer.ts

@@ -285,10 +285,15 @@ export class HeaderDrawerRenderer {
   }
 
   /**
-   * Handle drag leaving header - remove preview and restore source
+   * Handle drag leaving header - cleanup for grid→header drag only
    */
-  private handleDragLeave(_payload: IDragLeaveHeaderPayload): void {
-    this.cleanup();
+  private handleDragLeave(payload: IDragLeaveHeaderPayload): void {
+    // Only cleanup for grid→header drag (when grid event leaves header back to grid)
+    // For header→grid drag, the header item stays as ghost until drop
+    if (payload.source === 'grid') {
+      this.cleanup();
+    }
+    // For header source, do nothing - ghost stays until EVENT_DRAG_END
   }
 
   /**