fix: update loading state handling in CalendarPage and DutyList components

- Set isLoading to false in CalendarPage to prevent unnecessary loading indicators.
- Removed the loading spinner from CalendarHeader and adjusted rendering logic in DutyList to show a placeholder when data is not yet loaded for the month.
- Enhanced tests in DutyList to verify behavior when data is empty and when data is loading, ensuring accurate user feedback during data fetching.

webapp-next/src/components/calendar/CalendarHeader.tsx

@@ -30,13 +30,6 @@ export interface CalendarHeaderProps {
   className?: string;
 }
 
-const HeaderSpinner = () => (
-  <span
-    className="block size-4 shrink-0 rounded-full border-2 border-transparent border-t-accent motion-reduce:animate-none animate-spin"
-    aria-hidden
-  />
-);
-
 function isCurrentMonth(month: Date): boolean {
   const now = new Date();
   return (
@@ -82,16 +75,6 @@ export function CalendarHeader({
             aria-atomic="true"
           >
             {monthName(monthIndex)} {year}
-            {isLoading && (
-              <span
-                role="status"
-                aria-live="polite"
-                aria-label={t("loading")}
-                className="flex items-center"
-              >
-                <HeaderSpinner />
-              </span>
-            )}
           </h1>
           {showToday && (
             <button
@@ -116,10 +99,7 @@ export function CalendarHeader({
               disabled={disabled || isLoading}
               onClick={onRefresh}
             >
-              <RefreshCwIcon
-                className={cn("size-5", isLoading && "motion-reduce:animate-none animate-spin")}
-                aria-hidden
-              />
+              <RefreshCwIcon className="size-5" aria-hidden />
             </Button>
           )}
           <Button