Creates all-day container in header renderer

Ensures all-day container is created as part of the standard header structure, rather than on-demand.

Removes the request listener and logic for ensuring all-day container existence.

src/renderers/HeaderRenderer.ts

@@ -30,6 +30,10 @@ export class DateHeaderRenderer implements HeaderRenderer {
   render(calendarHeader: HTMLElement, context: HeaderRenderContext): void {
     const { currentWeek, config } = context;
     
+    // FIRST: Always create all-day container as part of standard header structure
+    const allDayContainer = document.createElement('swp-allday-container');
+    calendarHeader.appendChild(allDayContainer);
+    
     // Initialize date calculator with config
     DateCalculator.initialize(config);
     this.dateCalculator = new DateCalculator();