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>

Schemas/cta-post.json

@@ -148,9 +148,9 @@
         "button_text_color": {
           "type": "color",
           "label": "Texto boton",
-          "default": "#ffffff",
+          "default": "#0E2337",
           "editable": true,
-          "description": "Texto blanco para contraste"
+          "description": "Fase 4.4 Accesibilidad: navy-dark para contraste WCAG AA sobre fondo naranja"
         },
         "button_hover_bg": {
           "type": "color",