fix(accessibility): Update colors for WCAG AA contrast compliance

Phase 4.4 PageSpeed Accessibility fixes:
- cta-box-sidebar: title/description colors from white to navy-dark (#0E2337)
- contact-form: info_value_color from #D5D8DA to #495057, button text to navy-dark
- cta-lets-talk: text_color from white to navy-dark
- css-tablas-apu: .c3 column color from #6c757d to #495057 (7.0:1 ratio)

All changes ensure minimum 4.5:1 contrast ratio for normal text (WCAG AA).

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

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

Assets/css/css-tablas-apu.css

@@ -153,12 +153,13 @@
     text-align: left;
 }
 
-/* Columna 3: Unidad - centrada */
+/* Columna 3: Unidad - centrada
+   Fase 4.4 Accesibilidad: Color #495057 (ratio 7.0:1) en lugar de #6c757d */
 .analisis table td:nth-child(3),
 .analisis table td.c3,
 .desglose table td.c3 {
     text-align: center !important;
-    color: #6c757d;
+    color: #495057;
     font-size: 0.9em;
 }