fix: Mobile view improvements - accordion styling and modal centering

Fixed two critical mobile view issues:

1. Extended CV Sidebar Accordion:
   - Updated sidebar.html to use native <details> element (was div with onclick)
   - Styled accordion header to match CV title badges dark theme (#303030)
   - Applied consistent styling: dark gray background, light text, uppercase, no spacing
   - Result: Sidebars now collapse/expand properly with native HTML functionality

2. PDF Download Modal Centering:
   - Added JavaScript-based centering for mobile viewports (≤768px)
   - Uses inline styles with !important flag to override browser defaults
   - Updated download button to call openPdfModal() function
   - Result: Modal is perfectly centered on mobile (0px offset)

Technical notes:
   - Modal centering required setProperty() with 'important' flag
   - Accordion matches cv-title-badges-header style exactly
   - All tests passing: accordion toggle, modal centering

Files modified:
   - templates/partials/cv/sidebar.html
   - static/css/05-responsive/_breakpoints.css
   - static/js/main.js
   - templates/partials/widgets/download-button.html

Tests added:
   - tests/mjs/43-mobile-accordion-and-modal-test.mjs
   - tests/mjs/46-visual-accordion-style-test.mjs

templates/partials/widgets/download-button.html

@@ -5,7 +5,7 @@
     class="fixed-btn download-btn no-print has-tooltip"
     aria-label="{{if eq .Lang "es"}}Descargar PDF{{else}}Download as PDF{{end}}"
     data-tooltip="{{if eq .Lang "es"}}Descargar PDF{{else}}Download as PDF{{end}}"
-    onclick="document.getElementById('pdf-modal').showModal()"
+    onclick="openPdfModal()"
     _="on mouseenter call syncPdfHover(true)
        on mouseleave call syncPdfHover(false)">
     <iconify-icon icon="catppuccin:pdf" width="28" height="28"></iconify-icon>