Refactor renderer interfaces and update type names

Renames renderer interfaces to use 'I' prefix for clarity
Updates type references across related files
Improves type consistency in rendering strategies

src/renderers/DateHeaderRenderer.ts

@@ -0,0 +1,62 @@
+// Header rendering strategy interface and implementations
+
+import { CalendarConfig } from '../core/CalendarConfig';
+import { DateService } from '../utils/DateService';
+
+/**
+ * Interface for header rendering strategies
+ */
+export interface IHeaderRenderer {
+  render(calendarHeader: HTMLElement, context: HeaderRenderContext): void;
+}
+
+
+/**
+ * Context for header rendering
+ */
+export interface HeaderRenderContext {
+  currentWeek: Date;
+  config: CalendarConfig;
+}
+
+/**
+ * Date-based header renderer (original functionality)
+ */
+export class DateHeaderRenderer implements IHeaderRenderer {
+  private dateService!: DateService;
+
+  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 service with timezone and locale from config
+    const timezone = config.getTimezone();
+    const locale = config.getLocale();
+    this.dateService = new DateService(config);
+
+    const workWeekSettings = config.getWorkWeekSettings();
+    const dates = this.dateService.getWorkWeekDates(currentWeek, workWeekSettings.workDays);
+    const weekDays = config.getDateViewSettings().weekDays;
+    const daysToShow = dates.slice(0, weekDays);
+
+    daysToShow.forEach((date, index) => {
+      const header = document.createElement('swp-day-header');
+      if (this.dateService.isSameDay(date, new Date())) {
+        (header as any).dataset.today = 'true';
+      }
+
+      const dayName = this.dateService.getDayName(date, 'long', locale).toUpperCase();
+
+      header.innerHTML = `
+        <swp-day-name>${dayName}</swp-day-name>
+        <swp-day-date>${date.getDate()}</swp-day-date>
+      `;
+      (header as any).dataset.date = this.dateService.formatISODate(date);
+
+      calendarHeader.appendChild(header);
+    });
+  }
+}