[BE] FIX: 등록 가능 날짜 조회 시 해당 월의 첫 날 자정으로 수정

기존 시간설정을 하지 않아 조회 당일 기준보다 이전의 폼을 반환하지 않는 오류 수정

backend/src/main/java/org/ftclub/cabinet/presentation/service/PresentationService.java

@@ -41,7 +41,7 @@
 @Transactional(readOnly = true)
 public class PresentationService {
 
-	private static final Integer START_DAY = 1;
+	private static final Integer PRESENTATION_PERIOD = 3;
 	private static final Integer DEFAULT_PAGE = 0;
 	// 쿼리로 받?
 	private static final Integer MAX_MONTH = 3;
@@ -285,9 +285,10 @@ public void generatePresentationFormsEveryThreeMonth(LocalDate nowDate) {
 	}
 
 	public AbleDateResponseDto getAbleDate() {
-		LocalDateTime now = LocalDateTime.now();
+		LocalDateTime firstDateOfMonth = generateFirstLocalDateTime();
 		List<Presentation> dummyDates =
-				presentationQueryService.getDummyDateBetweenMonth(now, now.plusMonths(3));
+				presentationQueryService.getDummyDateBetweenMonth(firstDateOfMonth,
+						firstDateOfMonth.plusMonths(PRESENTATION_PERIOD));
 
 		List<LocalDateTime> result =
 				dummyDates.stream()
@@ -296,4 +297,12 @@ public AbleDateResponseDto getAbleDate() {
 
 		return new AbleDateResponseDto(result);
 	}
+
+	private LocalDateTime generateFirstLocalDateTime() {
+		return LocalDateTime.now()
+				.withDayOfMonth(1)
+				.withHour(0)
+				.withMinute(0)
+				.withSecond(0);
+	}
 }