Refactors all-day event rendering and DOM access

Decouples all-day event rendering, making it reactive to header readiness with period data.
Eliminates explicit DOM element caching, simplifying element access.
Enhances the `header:ready` event payload with `startDate` and `endDate`.
Improves all-day row height animation and calculation.

src/types/EventTypes.ts

@@ -85,4 +85,12 @@ export interface DragMouseLeaveHeaderEventPayload {
   mousePosition: MousePosition;
   originalElement: HTMLElement| null;
   cloneElement: HTMLElement| null;
+}
+
+// Header ready event payload
+export interface HeaderReadyEventPayload {
+  headerElement: HTMLElement;
+  startDate: Date;
+  endDate: Date;
+  isNavigation?: boolean;
 }