Separates all-day event rendering; handles header lifecycle

Event rendering strategies now exclusively handle timed events, while all-day events are managed by a dedicated renderer.

Centralizes calendar header creation within `GridRenderer`, ensuring the header element is always present from initial DOM construction. `HeaderManager` and `ScrollManager` now react to a `header:ready` event, which signifies the header is fully initialized.

Synchronizes all-day event rendering with header readiness, temporarily queuing events until the header is prepared. Emits an `allday:checkHeight` event to prompt all-day container height adjustments after rendering.

src/managers/AllDayManager.ts

@@ -120,6 +120,12 @@ export class AllDayManager {
       // Recalculate all-day height since clones may have been removed
       this.checkAndAnimateAllDayHeight();
     });
+
+    // Listen for height check requests from EventRendererManager
+    eventBus.on('allday:checkHeight', () => {
+      console.log('📏 AllDayManager: Received allday:checkHeight request');
+      this.checkAndAnimateAllDayHeight();
+    });
   }
 
   /**