更新消息列表UI

This commit message summarizes the following changes:

* Removed `BottomNavigationPlaceholder` and replaced it with a `Spacer` to manage bottom
 spacing.
* Removed unnecessary `Spacer` and adjusted spacing around comment items for better visual layout.
* These changes improve the user interface of the message list.

app/src/main/java/com/aiosman/riderpro/ui/index/tabs/message/MessageList.kt

@@ -152,7 +152,7 @@ fun NotificationsScreen() {
                         }
                     }
                     item {
-                        BottomNavigationPlaceholder()
+                        Spacer(modifier = Modifier.height(72.dp))
                     }
                 }
             }
@@ -331,7 +331,6 @@ fun CommentNoticeItem(
 
             }
             Spacer(modifier = Modifier.width(24.dp))
-//        Spacer(modifier = Modifier.weight(1f))
             commentItem.post?.let {
                 CustomAsyncImage(
                     context = context,