Enables event resizing via drag handles

Adds a resize handle manager to handle mouse hover
effects on calendar events and display a resize indicator.

This allows users to visually identify and initiate
event resizing by hovering near the bottom edge of an event.

src/types/ManagerTypes.ts

@@ -13,6 +13,7 @@ export interface CalendarManagers {
   calendarManager: CalendarManager;
   dragDropManager: unknown; // Avoid interface conflicts
   allDayManager: unknown; // Avoid interface conflicts
+  resizeHandleManager: ResizeHandleManager;
 }
 
 /**
@@ -70,6 +71,10 @@ export interface AllDayManager extends IManager {
   [key: string]: unknown; // Allow any properties from actual implementation
 }
 
+export interface ResizeHandleManager extends IManager {
+  // ResizeHandleManager handles hover effects for resize handles
+}
+
 export interface ResourceData {
   resources: Resource[];
   assignments?: ResourceAssignment[];