Refactors DateCalculator to be a static class

This change refactors the DateCalculator class to be a static class.
This removes the need to instantiate DateCalculator in multiple
managers and renderers, simplifying dependency management and
ensuring consistent date calculations across the application.
The configuration is now initialized once at the application start.

src/index.ts

@@ -3,6 +3,7 @@ import { eventBus } from './core/EventBus.js';
 import { calendarConfig } from './core/CalendarConfig.js';
 import { CalendarTypeFactory } from './factories/CalendarTypeFactory.js';
 import { ManagerFactory } from './factories/ManagerFactory.js';
+import { DateCalculator } from './utils/DateCalculator.js';
 
 /**
  * Initialize the calendar application with simple direct calls
@@ -13,6 +14,9 @@ async function initializeCalendar(): Promise<void> {
     // Use the singleton calendar configuration
     const config = calendarConfig;
     
+    // Initialize DateCalculator with config first
+    DateCalculator.initialize(config);
+    
     // Initialize the CalendarTypeFactory before creating managers
     CalendarTypeFactory.initialize();