Fix: remove duplicate author-bio includes, add author images, move inline styles

- Remove author-bio.php and article-footer.php duplicate inclusions from
  inside related article cards across 17 articles (was rendering 4x per page)
- Create /assets/images/authors/ with SVG avatars for all 7 named authors
- Move inline <style> block out of author-bio.php into main.css

assets/images/authors/sarah-chen.svg

@@ -0,0 +1,5 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="80" height="80" viewBox="0 0 80 80">
+  <circle cx="40" cy="40" r="40" fill="#144784"/>
+  <circle cx="40" cy="30" r="14" fill="rgba(255,255,255,0.9)"/>
+  <ellipse cx="40" cy="68" rx="22" ry="18" fill="rgba(255,255,255,0.9)"/>
+</svg>