Add Event Calendar feature with event occurrences service integration

Introduced a new Event Calendar component that displays scheduled events using the Heron.MudCalendar. Implemented IEventOccurrenceService to fetch event occurrences, and added mock data for initial testing. Updated navigation menu to include a link to the Event Calendar.

WebApp/Program.cs

@@ -172,6 +172,7 @@ builder.Services.AddDatabaseDeveloperPageExceptionFilter();
 
 builder.Services.AddScoped<ClipboardService>();
 builder.Services.AddScoped<WebApp.LocalStorageService>();
+builder.Services.AddScoped<WebApp.Services.IEventOccurrenceService, WebApp.Services.EventOccurrenceService>();
 
 // State container for maintaining state per user connection (Blazor Server)
 builder.Services.AddScoped<StateContainer>();