fix(accessibility): Fix cta-post contrast and heading hierarchy

Phase 4.4 Accessibility fixes:
- cta-post: button_text_color from #ffffff to #0E2337 (WCAG AA 4.8:1)
- TableOfContentsRenderer: h4 toc-title changed to span (semantic)
- FooterRenderer: h5 widget-title changed to span (5 instances)

Fixes: "Low contrast on cta-button" and "Headings skip levels"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Public/TableOfContents/Infrastructure/Ui/TableOfContentsRenderer.php

@@ -384,7 +384,7 @@ final class TableOfContentsRenderer implements RendererInterface
         $html = '<div class="toc-container">';
 
         $html .= sprintf(
-            '<h4 class="toc-title">%s</h4>',
+            '<span class="toc-title d-block h4">%s</span>',
             esc_html($title)
         );