Feat: Ejemplo menú nav con navegación accesible

[ctrl-alt-d]

Accessible Navigation Component

Summary

This PR implements a fully accessible navigation system following WCAG 2.1 guidelines, based on the accessible-astro-starter patterns.

Changes

New Components

• Navigation.astro - Main accessible navigation with full keyboard support
• ResponsiveToggle.astro - Mobile menu toggle button with proper ARIA attributes
• Based on: https://github.com/incluud/accessible-astro-starter

Refactored

• Nav.astro - Simplified wrapper that imports the Navigation component
• Moved components from src/layouts/components/ to src/components/ (Astro convention)

Accessibility Features

Keyboard Navigation (Desktop)

Key	Action
Tab	Navigate between focusable elements
ArrowLeft / ArrowRight	Move between top-level menu items (closes open dropdowns)
ArrowDown	Open dropdown and focus first item
ArrowUp / ArrowDown	Navigate within dropdown items
Enter / Space	Open dropdown and focus first item
Escape	Close dropdown and return focus to trigger

Mobile Navigation

• Uses native <details> / <summary> elements for expandable menu sections
• No complex JavaScript required for accordion behavior
• Escape closes the entire mobile menu
• Simple <a> links for all menu items

ARIA Support

• aria-expanded on dropdown triggers
• aria-haspopup on buttons with submenus
• aria-controls linking buttons to their menus
• aria-current="page" on active menu items
• aria-label on navigation landmarks