Fix accessibility violations: color contrast, aside nesting

- Improve text contrast from #666/#888/#999 to #555/#6b6b6b across site (WCAG AA)
- Fix aside nesting in all 10 blog articles (aside→div in related-articles)
- Fix aside nesting in quote sidebar
- Update CRO enhancement CSS/JS inline colors

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

assets/css/main.css

@@ -4653,7 +4653,7 @@ body { font-size: 17px; }
 
 .bio-role {
     font-size: 0.95rem;
-    color: #666;
+    color: #555;
     margin: 0 0 12px 0;
     font-weight: 500;
 }