refactor(ranking): 주차 계산 로직 개선

- ISO 주차 기준으로 변경하여 일관성 있는 주차 계산 보장

Author: hyujikoh

apps/commerce-api/src/main/java/com/loopers/interfaces/api/ranking/RankingV1Controller.java

@@ -77,9 +77,9 @@ private String processYearWeekParameter(String yearWeek, LocalDate date) {
         // date가 있으면 해당 날짜의 주차, 없으면 현재 주차
         LocalDate targetDate = date != null ? date : LocalDate.now();
 
-        WeekFields weekFields = WeekFields.of(Locale.getDefault());
+        WeekFields weekFields = WeekFields.ISO;
         int year = targetDate.getYear();
-        int week = targetDate.get(weekFields.weekOfYear());
+        int week = targetDate.get(weekFields.weekOfWeekBasedYear());
 
         return String.format("%d-W%02d", year, week);
     }