fix activity posts not marked as read (#2008)

we cache posts for 1 day, so we have to account for that by making sure that in 1 day none of the posts we have cached exceed the active-days constant. otherwise they don't get marked as read.

TASVideos.Core/Services/ForumService.cs

@@ -254,7 +254,7 @@ public async Task<int> CreatePost(PostCreate post)
 			return forumActivity;
 		}
 
-		DateTime minimumDate = DateTime.UtcNow.AddDays(-ForumConstants.DaysPostsCountAsActive);
+		DateTime minimumDate = DateTime.UtcNow.AddDays(-(ForumConstants.DaysPostsCountAsActive - 1)); // we subtract 1 day here because we cache activity for 1 day
 
 		var fullrow = await db.ForumPosts
 			.Where(fp => fp.CreateTimestamp > minimumDate || fp.PostEditedTimestamp > minimumDate)
@@ -306,7 +306,7 @@ public async Task<int> CreatePost(PostCreate post)
 			return subforumActivity;
 		}
 
-		DateTime minimumDate = DateTime.UtcNow.AddDays(-ForumConstants.DaysPostsCountAsActive);
+		DateTime minimumDate = DateTime.UtcNow.AddDays(-(ForumConstants.DaysPostsCountAsActive - 1)); // we subtract 1 day here because we cache activity for 1 day
 
 		var fullrow = await db.ForumPosts
 			.Where(fp => fp.CreateTimestamp > minimumDate || fp.PostEditedTimestamp > minimumDate)