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>

case-studies/index.php

@@ -26,7 +26,7 @@ $canonical_url = "https://ukaiautomation.co.uk/case-studies/";
         .cs-card-body { padding: 30px; }
         .cs-tag { display: inline-block; background: #f0f9f7; color: #4f46e5; font-size: 0.8rem; font-weight: 600; padding: 4px 12px; border-radius: 20px; margin-bottom: 16px; text-transform: uppercase; letter-spacing: 0.5px; }
         .cs-card h2 { font-size: 1.3rem; color: #1e1b4b; margin-bottom: 12px; }
-        .cs-card p { color: #666; line-height: 1.6; margin-bottom: 20px; }
+        .cs-card p { color: #555; line-height: 1.6; margin-bottom: 20px; }
         .cs-result { background: #f8f9fa; border-radius: 8px; padding: 16px; font-weight: 600; color: #7c3aed; }
         .cs-result span { display: block; font-size: 1.5rem; color: #6d28d9; }
         .cs-cta { padding: 80px 0; background: linear-gradient(135deg, #7c3aed 0%, #6d28d9 100%); text-align: center; color: white; }