fix: remove duplicated headers from blog post bodies

- remove extracted title, byline, date, avatar, and featured image preambles
- prevent both extraction scripts from recreating duplicated headers
- add blog content duplication auditing
- update migration documentation

www/reports/blog-content-audit.md

@@ -0,0 +1,5 @@
+# Blog Content Audit
+
+Checked 65 blog post bodies for layout content duplicated in Markdown.
+
+No duplicated article headers were detected.

www/reports/cleanup-log.md

@@ -27,5 +27,9 @@
 - Restored the live library banner and consultation form section background.
 - Added a mapped-page-imagery audit to prevent missing visual assets from
   silently passing the source link audit.
+- Removed duplicated article titles, author/date blocks, and featured images
+  from all 65 blog Markdown bodies; these elements are rendered by the shared
+  blog-post layout. Updated both extractors and added a blog-content audit to
+  prevent recurrence.
 - Added language-qualified content collection IDs to prevent English, Spanish,
   and Arabic entries with the same slug from overwriting each other.

www/reports/migration-summary.md

@@ -114,6 +114,8 @@ unavailable.
   Markdown links, and public assets when rendered output is unavailable.
 - `npm run audit:images`: passed with no missing mapped page banners, section
   backgrounds, or blog featured images.
+- `npm run audit:blog`: passed with no article-header content duplicated in
+  blog Markdown bodies.
 - `npm run generate:sitemap`: passed; generated 97 URLs.
 - `npm run generate:redirects`: passed.
 - All migration `.mjs` tools and the sandbox DNS helper pass `node --check`.