Refactor calendar datasource and event management

Enhances calendar flexibility by introducing group-based column spanning and improving cross-mode event handling

Adds support for:
- Dynamic column grouping in date and resource modes
- Consistent event drag-and-drop across different calendar views
- More robust all-day event layout calculations

Improves event management logic to handle resource and date mode transitions more elegantly

src/types/ColumnDataSource.ts

@@ -9,6 +9,7 @@ export interface IColumnInfo {
   identifier: string;           // "2024-11-13" (date mode) or "person-1" (resource mode)
   data: Date | IResource;       // Date for date-mode, IResource for resource-mode
   events: ICalendarEvent[];     // Events for this column (pre-filtered by datasource)
+  groupId: string;              // Group ID for spanning logic - events can only span columns with same groupId
 }
 
 /**
@@ -40,6 +41,11 @@ export interface IColumnDataSource {
    */
   setCurrentDate(date: Date): void;
 
+  /**
+   * Get the current date
+   */
+  getCurrentDate(): Date;
+
   /**
    * Update the current view (day/week/month)
    * @param view - The new calendar view

src/types/EventTypes.ts

@@ -43,6 +43,8 @@ export interface IDragEndEventPayload {
   originalSourceColumn: IColumnBounds;  // Original column where drag started
   finalPosition: {
     column: IColumnBounds | null;  // Where drag ended
+    date: Date;                     // Always present - the date for this position
+    resourceId?: string;            // Only in resource mode
     snappedY: number;
   };
   target: 'swp-day-column' | 'swp-day-header' | null;