H1 Detection Improvements:
- Post title now counts as H1 (most themes render it that way)
- New 'title_is_h1' option (default true)
- Fixed false positive "No H1 detected" when post has a title
- Better warning when H1 exists in content alongside title
- Improved heading hierarchy validation (content should start with H2)

Post List Column Fix:
- Fixed column not showing for posts/pages
- WordPress uses 'manage_posts_columns' not 'manage_post_posts_columns'
- Same fix for pages ('manage_pages_columns')

New Features:
- Added image alt text detection ('detect_missing_alt' option)
- Shows count of images missing alt text for accessibility/SEO