feat(blog): add subscription-only blog post detection and UI updates

Add HasSubscriptionOnlyBlogPosts function to check if a repository has premium blog content. Update subscribe page to display different messaging when paid blogs are available. Redesign featured blog section with centered layout, larger images, and improved hover effects.

models/blog/blog_post.go

@@ -410,6 +410,12 @@ func CountPublishedBlogsByRepoID(ctx context.Context, repoID int64) (int64, erro
 	return db.GetEngine(ctx).Where("repo_id = ? AND status >= ?", repoID, BlogPostPublic).Count(new(BlogPost))
 }
 
+// HasSubscriptionOnlyBlogPosts returns true if the repo has any published subscription-only blog posts.
+func HasSubscriptionOnlyBlogPosts(ctx context.Context, repoID int64) (bool, error) {
+	count, err := db.GetEngine(ctx).Where("repo_id = ? AND status >= ? AND subscription_only = ?", repoID, BlogPostPublic, true).Count(new(BlogPost))
+	return count > 0, err
+}
+
 // CreateBlogPost inserts a new blog post.
 func CreateBlogPost(ctx context.Context, p *BlogPost) error {
 	_, err := db.GetEngine(ctx).Insert(p)