Improves drag cancellation behavior

Implements drag cancellation when the mouse leaves the calendar container during a drag operation. This prevents orphaned drag clones and restores the original event's state, enhancing user experience.

All-day events now correctly recalculate their height upon drag cancellation, ensuring accurate rendering after clone removal.

Refactors HeaderManager by removing redundant caching of the calendar header element.

Adds new mock event data for September and October 2025 to expand testing and demonstration scenarios.

src/managers/DragDropManager.ts

@@ -62,6 +62,7 @@ export class DragDropManager {
   // Column bounds cache for coordinate-based column detection
   private columnBoundsCache: ColumnBounds[] = [];
 
+
   // Auto-scroll properties
   private autoScrollAnimationId: number | null = null;
   private readonly scrollSpeed = 10; // pixels per frame
@@ -108,6 +109,16 @@ export class DragDropManager {
     document.body.addEventListener('mousedown', this.boundHandlers.mouseDown);
     document.body.addEventListener('mouseup', this.boundHandlers.mouseUp);
 
+    // Add mouseleave listener to calendar container for drag cancellation
+    const calendarContainer = document.querySelector('swp-calendar-container');
+    if (calendarContainer) {
+      calendarContainer.addEventListener('mouseleave', () => {
+        if (this.draggedElement && this.isDragStarted) {
+          this.cancelDrag();
+        }
+      });
+    }
+
     // Initialize column bounds cache
     this.updateColumnBoundsCache();
 
@@ -303,7 +314,41 @@ export class DragDropManager {
   private cleanupAllClones(): void {
     // Remove clones from all possible locations
     const allClones = document.querySelectorAll('[data-event-id^="clone"]');
-    allClones.forEach(clone => clone.remove());
+    
+    if (allClones.length > 0) {
+      console.log(`🧹 DragDropManager: Removing ${allClones.length} clone(s)`);
+      allClones.forEach(clone => clone.remove());
+    }
+  }
+
+  /**
+   * Cancel drag operation when mouse leaves grid container
+   */
+  private cancelDrag(): void {
+    if (!this.draggedElement) return;
+
+    console.log('🚫 DragDropManager: Cancelling drag - mouse left grid container');
+
+    const draggedElement = this.draggedElement;
+
+    // 1. Remove all clones
+    this.cleanupAllClones();
+
+    // 2. Restore original element
+    if (draggedElement) {
+      draggedElement.style.opacity = '';
+      draggedElement.style.cursor = '';
+    }
+
+    // 3. Emit cancellation event
+    this.eventBus.emit('drag:cancelled', {
+      draggedElement: draggedElement,
+      reason: 'mouse-left-grid'
+    });
+
+    // 4. Clean up state
+    this.cleanupDragState();
+    this.stopAutoScroll();
   }
 
   /**