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

static/css/04-interactive/_modals.css

@@ -739,8 +739,23 @@
     }
 }
 
+/* Mobile keyframes - must be outside media query */
+@keyframes modalFadeInMobile {
+    from {
+        opacity: 0;
+        transform: translate(-50%, -50%) scale(0.9);
+    }
+    to {
+        opacity: 1;
+        transform: translate(-50%, -50%) scale(1);
+    }
+}
+
 /* Mobile: Single column - Button-like style */
-@media (max-width: 479px) {
+@media (max-width: 768px) {
+    /* Mobile centering is now handled via JavaScript in openPdfModal() */
+    /* This CSS provides fallback styling for mobile screens */
+
     .pdf-download-modal {
         max-width: calc(100% - 1rem);
     }