Adds event description support in calendar UI

Extends event model to include optional description field

Enhances event rendering with:
- New description getter/setter in base event element
- Updated CSS grid layout for description display
- Dynamic description handling in event rendering
- Updated mock event data with descriptions

Improves visual information density and event context in calendar view

src/types/CalendarTypes.ts

@@ -17,6 +17,7 @@ export interface IRenderContext {
 export interface ICalendarEvent {
   id: string;
   title: string;
+  description?: string;
   start: Date;
   end: Date;
   type: string;  // Flexible event type - can be any string value