Refactor calendar datasource architecture

Centralizes date calculation logic into DateColumnDataSource
Improves separation of concerns across rendering components

Key changes:
- Introduces IColumnInfo interface for flexible column data
- Moves date calculation from multiple managers to dedicated datasource
- Removes duplicate date rendering logic
- Prepares architecture for future resource-based views

src/types/EventTypes.ts

@@ -60,7 +60,7 @@ export interface IDragMouseEnterHeaderEventPayload {
 
 // Drag mouse leave header event payload
 export interface IDragMouseLeaveHeaderEventPayload {
-  targetDate: string | null;
+  targetColumn: IColumnBounds | null;
   mousePosition: IMousePosition;
   originalElement: HTMLElement| null;
   draggedClone: HTMLElement| null;