fix: use wrapped id instead of native id in BoardMember

Author: jamesjieye

src/main/java/com/taskagile/domain/model/board/BoardMember.java

@@ -22,12 +22,12 @@ public static BoardMember create(BoardId boardId, UserId userId) {
     return boardMember;
   }
 
-  public long getBoardId() {
-    return id.boardId;
+  public BoardId getBoardId() {
+    return id.getBoardId();
   }
 
-  public long getUserId() {
-    return id.userId;
+  public UserId getUserId() {
+    return id.getUserId();
   }
 
   @Override