Move engagement calculation inside widget

internal/feed/reddit.go

@@ -110,7 +110,5 @@ func FetchSubredditPosts(subreddit, sort, topPeriod, search, commentsUrlTemplate
 		posts = append(posts, forumPost)
 	}
 
-	posts.CalculateEngagement()
-
 	return posts, nil
 }

internal/widget/reddit.go

@@ -95,6 +95,7 @@ func (widget *Reddit) Update(ctx context.Context) {
 	}
 
 	if widget.ExtraSortBy == "engagement" {
+		posts.CalculateEngagement()
 		posts.SortByEngagement()
 	}