Improves all-day event drag and drop

Handles dragging of both timed events (converting to all-day) and existing all-day events to different days.

Refactors all-day height recalculation to support animated transitions for a smoother user experience when all-day event counts change.

Uses event delegation for header mouseover detection.

Updates ScrollManager to listen for header height changes.

src/managers/ScrollManager.ts

@@ -36,6 +36,10 @@ export class ScrollManager {
       this.setupScrolling();
     });
 
+    // Handle all-day row height changes
+    eventBus.on('header:height-changed', () => {
+      this.updateScrollableHeight();
+    });
     
     // Handle window resize
     window.addEventListener('resize', () => {