feat: qna createAT timestamp로 변경

backend/src/main/java/com/edufocus/edufocus/qna/entity/Qna.java

@@ -32,7 +32,7 @@ public class Qna {
 
 
     @Column(name = "created_at")
-    @Temporal(TemporalType.DATE)
+    @Temporal(TemporalType.TIMESTAMP)
     private Date createdAt;
 
     @Column(name = "modified_at")
@@ -53,5 +53,4 @@ public class Qna {
     private Lecture lecture;
 
 
-
 }